1) The Crafting(Frequency) specialization/bonus is dead. Crafting(Strength) is king. Long live the king.
Incorrect. Frequency spec affects the default for your items, so it applies its benefit for free across all of them, like the strength spec does. So if you have three one-use items, now you have three two-use items for one spec point.
That doesn't suck. Yeah, it's not as effective if you only plan to have one item, but if that's the case, you're clearly going to take strength anyway.
2) Just like an evocation, a item with Block:4 can be used as Armour:2. Unlike the evocation, both Block and Armour both burn a use.
Yeah, but in the case where the wizard changes his mind on a use because of how the dice roll out, I figure only a real jerk would charge him for two uses.
3) About stacking. I could enchant a Block:6 effect on a Armour:2 Kevlar jacket and if threated with a Weapon:2 attack I could choose to not invoke a use and let the jacket take the hit. If threatened by a stronger attack I could then invoke a use for the Block:6 or Armour:3 effect. When all uses have been burned it fails to jut Armour:2 until recharged.
That sounds right, yeah.