Don't go for WEU. your map won't be playable to other people withour WEU installed.
Megafyr, that statement is incorrect. It will be playable by everyone as long as they have WC3 uptodate and installed.
Use JNGP like Rui sujested, its like WEU with all the junk removed and more good things added.
A) Don't make 256x256 maps. I've never played a good one.
B) With a size like that, use doodads more sparingly. Tile variation is your best friend.
C) Yes, but it's not worth it. I can't remember what does, I don't think MiscData does, maybe WEU, or NewGen.