whoops and forgot Ramps are just special forms of windlass one floor deep if you think about it but see the problem with  overall number of crystals, maybe lift crystals quicker and easier to grow. Need 250. hmmmmmmm

Good Debate.
nothing says whether  they are floating or not specifically!
But text suggests, as pointed out above, it is on the surface.
It is also guarded. Pike says he was almost shot up after walking a mile across the surface with his injured crew. Indigenous wildlife get in through vents etc. Nothing described as flying but crawling climbing things we know of this suggests contact with the ground or only flying or things that jump high.

By the way what was Pike and his crew up to?  Did he crash a mile out from the spire?  That's damned close. Why did he crash? He's a regular has his own suite.  Is Jim leaving another of his plot threads waving in the air?. Is this a "car crash" we will get back to in Book 6?

I look but cant find reference in the book to a conversation that says electricity is not supplied to the habbles. Would appreciate someone [Please pointing it out to me.  How habbles function intrigues me. They need power.
As for defense. The spirearch makes clear he cannot trust the Guard till the traitorare flushed. Also they are police he gives the numbers and points out they are stretched thin over 236 habitted habbles. He has to let things play out without any obvious response from himself other than the sending of a small secret force.
The Fleets defensive strategy I've explained is down to Wilson. As to his genius Bayard and Grimm may have been ironic! There are clearly lots of problems within the fleet. If Jim is modelling the British Admiralty over its history then there's internal battles over Aristocratic Command structures mostly by baffoons buying their positions versus professional seaman earning command [Rook]. In any event he Wilson was thinking invasion not guerrilla warfare.
500  highly trained Marines vs 96 Grimms Crew [minus casualties as the book progresses]. Plus the Silkweavers [1000?] Grimm is outnumbered and has to be reactive following the marines  not taking them on one on one. He is ordered to protect Ferus group that's important  he cant defend the landing and do that with the resources he has. He also has no idea what the marines will do next.
  By the time he gets to the Monastery they are attacking the Habble itself on the way to the landing.
Predator is barely functional and only manages to get up to battle ready by the skin of her teeth and survive the destruction of the landing. [Also thanks to Ransoms empathetic nostalgia...  big mistake by her but revealing another side to her than pure mercenary] If he made an Alamo of Predator with no shroud, Mistshark would have blown her to hell and back nostalgia or no.
Never mind some approx 350 to 400 trained Marines heavily armed with explosives playing in a tinderbox of wood. Turns out he makes the right calls to save the group and eventually reveal [and in some way yet to be explained in full] deadened the impact of the reason behind the whole Aurorean attack which was acquiring the Index.
Also haven't specifically timed everything but main events in whole book is over a couple of days i"d say. There's no time to particularly put the Spire on a war footing never mind that for his own reasons the Spirearch has kept the information suppressed. So who knew ... a handful of people in the spire and the fleet outside it.
Any defensive cannon on the landing would have been targetted and blown up by the marines and remember its all wood not even spirestone so ridiculously vulnerable from an internal attack.
sorry but it is pearl harbor'ish'. in and out quick have a plan stick to it no invasion  just the damage which in this case was a plus to the real objective the Index.  Look at the fall of Singapore or the Maginot line for "almost" parallels of defenses pointing the wrong way.

As for Iron rot... love it It applies to both sides seriously handicaps armed warfare sets limits makes for interesting world building. I suggest Jim has thought through the implications and is having fun with the problem he has set himself.

my thoughts
Its a Wayist Document and they are independent of spires. If the book was not a public document it can be assumed it contained information the Wayist and /or some other power/organisation wanted kept secret/. Its existence would have been suspected and maybe its nature but not the contents. For example the Spirearch does not seem surprised when given 2 copies and recognises its importance. As far as we know Ferus showed no interest in it yet Cavandish did so  its not necessarily something central to an etherealist. So means to an ends rather than having any power in itself and Cavandish was securing it for the Aurorans or for her Master. Its value it seems is in the content remaining secret  now its in Cavandish's memory and in her physical copy the actual book she had is irrelevant. That Albion has it is of no concern. Also of interest given that she has memorised it she does need a physical copy. In her memory it would make her more important but she cant risk that or she wont defy orders to provide a physical copy.
Content is names clearly burning the copies is an attempt to delay the knowledge of the content from being known to others but not an absolute necessity or Cavendish would have destroyed her copy when memorised. The burning of the Monastery is a definite primary  target of the incursion of the marines sending a message to others and acquiring the Index. Destroying copies useful but as subsequent actions of hers shows not absolutely essential.She wants more copies in her control as she orders for Marines to make copies. She is not worried about the marines seeing or knowing the names. Either because she is planning to kill them  or because the names as such are meaningless to them. Some other knowledge or context is needed to make sense of the names. The index is some link in a chain. That the Spirearch doesn't open to read suggests he knows this is not immediate knowledge he needs or not immediately available to him simply by reading.
Names can be of things and of people. Which, really we have no clue and can be of both ie names of Spires and of people in them.  From the  mass of pages on her table  on to which Cavendish was  copying her memory  the index was a book of some size and therefore a large number of names
By the way we only have Cavendish's statement that it contains names, is that all it contains, is she lying?
"An index is an indirect shortcut derived from and pointing into a greater volume of values, data, information or knowledge"
That its called an index  suggests the latter part  shortcut to information or knowledge. Names of other books people who hold knowledge or where it can be found. There is a suggestion of secret knowledge and not much of a stretch to associate that with the Builders and what will unfold as a race to its discovery.

WHOOPS HERE WE GO AGAIN!

"Habble Morning occupied the entirety of the spire  most of it beneath a vast atrium nearly 200 feet high and it was the next best thing to 2 miles from one side of the  great cylinder that was the spire Albion to the other. Ch 14"

Hmmm  Cylinder  but  but means square in circle and not as map [circle in square] and not a Borg cube!!!!!
Plus
 200 foot atrium  room for 3 habbles and decreases the available space for 250 habbles spaced 50 feet apart [which is tight anyway]  The need to get the 250 habbles into a spire needs about two and half miles allowing for variations like this atrium  ie how thick are the floors  10 feet   that would give another  2,480 feet to account for. Grins sorry Jim i'm being pedantic  and I guessing the spires are in of themselves  important to your story  so would  be nice to get them right and as an arcology
its an exciting idea for a living environment.

Each spire is  a square with sides of 2 miles and therefore a floor area of 4 square miles. The Spirearch of Albion states Albion is ten thousand feet high and has 250 habbles of which 236 are occupied. Each habble is quoted as 50 feet floor to ceiling. This has to assume that the none inhabited  habbles are somewhat less that 50 feet high in order to fit within 10,000 feet overall height [1.89 miles].It is possible the Spirearch is generalising  the dimensions and the spire is a black  tower 2 miles high. There are references to a 2 mile fall for aeronauts. The living use-able floor area of each habble is a circle with a 2 mile radius. This then allows for various utilities and engineering needs at the periphery of each habble. It is possible that some habbles are not used for habitation and do not require a 50 foot ceiling. But the design is by the builders so it would presumably be uniform given the building material seems indestructible. To fit the 250 habbles need at 50ft ceilings would need  a height of about 12,000 feet [2.27 miles].
As the spirearch  is simply making a point of the complexity of the Albions spire he needn't have to be precise. Its 2x2 dimension  needs to be to be a square but to grow a cylinder on that base and to still be symmetrical  the height is immaterial. A spire normally tapers from that square, clearly these don't but can still call them spires why not.

Jim talks in his public appearances of the spires as Borg cubes. Which sort of destroys any visual image as a spire which has to at least be taller than wide and should taper but a square based tower ie rectangle  would sort of cover a spire. In the book chapter 33 further confusion as the spires are described round with the habbles having a square floor plan fitting inside. This contradicts the maps drawn for the books which reverse  to square containing circle.
Perhaps its pedantic and can be dismissed as the characters Bridget in this case having no real idea of geometry and having never gone outside to see the actual shape of the spire. Whether the earth is flat or round matters very little to most people in conducting their day to day lives.
But editing should have spotted this for Jim.

What interests me is  the sub title of the series  the cinder spires. Cinder is slag something left over after a process  iron slag coal slag  etc  cinders. As a verb to slag something is to reduce it to rubble.  So Jim, made from slag or are we venturing into the future not the past.