My answers, for what they're worth:
Armageddon
Seems as though it would 'work', but be ineffective or even counterproductive. Angelic spirits have no need for help to appear anywhere they wish, but their ability to act is limited by their natures. So they would be unable to act unless they were destined to act, in which case they would have done so without the need to be summoned. On the downside, you have succeeded in drawing them away from what they *were* intended to do...
Blinding Glory
I think that as you've worded this, it might act basically only as a disguise of sorts. That is, people would be able to look at everything normally, but they would only gain perception-based information from everything *except* you. They would, in effect, see a person-shaped nothingness (or in this case, a brightness). But since you aren't actually *attacking* them in any way (you aren't producing a blindness affect, for example), they would still recognize that there is *something* there. Put in other words, you are sort of casting an illusion over yourself, replacing your image with that of a bright (but not actually blindingly so) light. So they could, for example, still shoot at 'the light' if they were so inclined. And I think it would be a light/illusion spell, rather than a veil (which is stealth-based and the opposite of the effect you are creating.
Then again, perhaps it is more of a 'special effect' alteration of the standard veil.
Fires of Heaven
I think that this would work. That is, it would basically create a new "permanent" location aspect for the area defined by the spell. It wouldn't be the same as a ward or threshold, exactly, but creatures that are adverse to holy power could be subject to compels against their high concept when entering the area. Note, though, that the permanency is relative, since the aspect could still be removed fairly easily. Since it is a maneuver (albeit a very prolonged sticky one), it can be removed by a mere maneuver (as can all maneuver-created aspects). I think that I'd probably require that this manuever be done by someone who was not adversely impacted by the aspect. For example, a RCV would be unable to enter the area due to the compel. But the RCV could hire/coerce a non-vampire into performing a "desecration" maneuver (thus removing the aspect) in the area for them.
Metafaculty
Thaumaturgy can do lots of cool things, but it can't simply manufacture answers from thin air. You need to figure out where the answers are coming from, then narrate how your spell gets them. You can get information about a particular subject (for example, where they are, what apsects they have, etc) by making use of the simple action and assessment capabilities. You can gain knowledge about a subject by summoning a knowledgable entity and getting answers from them by some means. You can even look into the future, or the past, or read people's thoughts, so long as you're willing to accept the consequences. But you can't simply cast a spell that generates knowledge from nothing, in my opinion. Keep in mind that even if you worked the spell as a simple action Lore result of 20, the information gleaned would be limited to the arcane library used in conjunction with the research attempt. So most information spells are about gaining access to a superior information source (like a intellect spirit or demon or such) and then hiring or coercing them to provide you with the knowledge you want.
Microcosm
I think that this sort of spell is probably feasible, though it would certainly constitute mind magic rather than a veil, along with the baggage that accompanies it. That is, you are actuallymaking changes to the workings of their mind and memories, rather than simplying altering the information that enters their perceptions. At least, I think that's what you're trying to do. If, on the other hand, you are basically trying to create a sort of 'virtual reality' spell, completely controlling everything the target senses, then I think you're in the clear. But this sort of spell wouldn't impact at all what the target has already experienced.
The Pearly Gates
The conjuration rules are so incredibly hand-wavy that it's hard to comment on the subject. That said, a reality check: a wall of granite (for example) that was 10m high, 5m wide, and 4km long (which is a bit smaller than the wall you suggested and a bit longer that the wall around Jerusalem, as an arbitrary example), would require about a half million metric tons of granite. A single metric ton is not unusually large or small for a car. So we're talking about a half a million cars worth of mass here. I'm not saying that that your numbers aren't reasonable (after all, the examples they give in the book don't really make sense, either).
Oh, and a counterspell would turn it to rapidly dissolving goo. So pray that the attacking Mongols don't have a spellflinger with them.
Sword of Damocles
"Landmine" spells are based on wards, which are immobile. See YS276-277. That said, doesn't an Oath provide some of this same functionality?
True Creation
Same drawbacks as above, specifically and primarily that conjured items are vulnerable to counterspells. I also don't believe that soulfire itself can be conjured, so no manufacturing of magic items. That said, a GM could possibly allow a soulfire-based enchanment to be used as an 'excuse' to create an IoP. It probably should be a fairly low-powered one (Swords of the Cross have a LOT more mojo behind them than you can channel), and would still cost refresh if you tried to wield it.