1) Henchmen can barter, yes. They don't have reputation though afaik, so assuming you have a positive reputation, attitude and vendor prices may be more favourable for a PC with bartering. Crafting, blacksmithing, all possible if you prefer to leave non-combat skills to henchmen etc. (breaks roelplaying but if that isn't an issue for you, 1 is fine)
2) Probably cheaper. Depends if you buy or make the blank skillbook and scroll I guess.
3) Random afaik. If you really want one of those pieces of loot, you can check vendors for them periodically (saw a vendor selling a +1 crafting belt for example) and don't sell the ones you do find. There's a good thread (which I've avoided because I want to find out for myself) about crafting recipes in the forum
HTH
