1. Phwoar, some of your info is 5 years out of date, you're talking about crt_emudriver v1.2 for Catalyst 6.5 or 9.3, and using windows XP. Take a look at the crt_emudriver v2.0 download thread on Calamity's site, there's a list of compatible cards in the top post. Then also look at post 2 and work out if you need composite sync. Then read the Atom-15 thread on that same forum and work out if you need Atom-15, and if you do, start using google for any card or setup to find out if anyone's having problem with it using Atom-15.
http://geedorah.com/eiusdemmodi/forum/viewforum.php?id=72. In theory APU's work fine, if they're on the list. But in practice i'm not sure there's been much testing done. A discrete card is safer.
3. A nice, low-end R7 card should be great for what you want, but it's up to you and what you can get within budget that does the job you need. (see 1. above)
4. Yes, yes, and yes.