Alto,
1: Assuming the full game is the same as the demo, all items (and probably including scrolls) are randomized for each vender. So it is doubtful anyone can tell you where a scroll of resurrection is sold. I havn't found one yet (Level 17) so I am not even sure if they exist.
2: So far, I have only found that one tent that sells Horsemen, and only one other vender that sold a whopping 3 Knights. It forces you to diversify and use other troops. I usually ended up using the Horde units (other than peasents) to restock along with Priests and Thorn-Hunters(tons of damage once you get enough, plus there is an awesome helm that doubles thier damage and halves Rage loss). Once I got off the first continent I found that it was a good idea to Garrison your troops at the first Castle you find and start using what they are selling, because it saves you trips back and forth in the long run.
3: No clue, I havn't found any set items yet as far as I know. Not even sure if they exist.
4: You can't do much about the wife unless you divorce her. I think the babies are completely random so if you don't like her abilities or the kids have crappy mods then you give her the boot once you find a replacement. She takes a fifth of your money and whatever gear you leave on her, so I recommend stripping her before divorcing. Save your game first though, because I read there is a bug where if you equip an item she was wearing it crashes the game.
Any other questions?
EDIT: To answer your most recent question, once you are able to scribe a spell, may want to just start selling them all off at castles. If you can't scribe it yet just sell any duplicates.