He looks a little old, IMO. Ramirez is 20 in DB per WoJ, so he's 17 in his first appearance in SK. I considered Thomas Dekker for the role, but he's not hispanic.

It would depend on how closely they followed the books (religiously i hope), but he could do Harry plus an array of the side characters that only show up once in a while. 

Often, but not always.  Futurama, for example, always impressed me with the breath of characters a given VA could cover.

Remember that really great yet short lived series Kings?  It was a modern day adaptation of the biblical story of David.  It was cancelled partly for costing what was called an "extravagant" sum of 10mil for the pilot and 4mil per episode (same as fringe, far less than boardwalk empires).  Most of that went to the set/location rentals.  It also tried an experimental and ultimately terrible marketing strategy. 

In fact, I have to admit that I like the show better than the books.

Before you worry about defensive items and frequency of use, consider this - you'd only lose one "use" of the effect whenever it needs to be triggered, not every time you defend. If you dodge an attack, that doesn't use up energy - it only applies if you get hit and the item is what blocks/absorbs the hit.

So it makes defensive magical items more of a mystical ass-saving measure, which feels a lot more like how it's described in the books - it's Harry's last resort for when he can't dodge or otherwise protect himself. "Luckily, the blade was stopped on the flaps of my enchanted duster, or I'd have been a dead man," etc.

So would Harry's coat (made with Great Lore, and one item slot) be something like:

The coat provides either a Fair (+2) Block or Armor: 1 up to 5 times per session?

Because that's as close as can be gotten with it's current statting, but this version (made with Great Lore and two item slots) looks closer:

The coat provides either a Great (+4) Block or Armor: 2 up to 3 times per session.