1) IMO, with RTW. exe or BI.exe the AI on Hard or Very Hard Campaign difficulties hires too many mercenaries. Especially the AS and the Ptolies. Prepare to find your desired unit of Thraikioi Prodromoi in enemy hands before you can hire it yourself.
Perhaps the Alex.exe makes things better.

2) No idea.

3) Same problem here. And I use XP (Vista is evil).