I've read advance wars is not computerisable on PSP emus aka they get errors and slowdown and text errors?
1. You wont know unless you try. So get jGPS or whatever its called and try that first. Get both roms, its possible that one runs better than the other.
2. Advance wars for the GBA are ok. If you want the best "Advance wars" experience, you actually want to play the 2005 Duel Strike version. Do you have a 3DS compatible DS flash cart? If the answer is no, then I would suggest looking for a DSTWO. That way you can play the DS releases as well as get a the GBA emulator for DS and try the GBA ones that way.
3. My favorite Advance Wars game is actually the one that departs the farthest from the series, Days of Ruin. Its like the gritty reboot that does a good job, but is actually where the series stops. at least for the time being, unfortunately.