Hi, you made a great choice the PSP is an amazing piece of hardware for emulation and has a crawling library of good games (essential thread here
http://gbatemp.net/t300934-new-essentials-...ation-portable)
First i suggest you stick with your permanent custom firmware 6.39 PRO B8 (you already have the best there is but if you are interested in different options read here
http://gbatemp.net/t293978-how-to-softmod-hack-your-psp)
Personnaly i use the non-permanent 6.39 because Fast Recovery is perfectly fine for just 10 second at PSP launch and my PSP is model 3000.
Then you can get emulators here
http://gbatemp.net/t224035-psp-retro-emulators
The best being the ones for : Genesis, Nes, GB-GBC-Master System-GameGear all in 1 emulator, SNES, GBA, CPS1&2 (arcade capcom) and MVSPSP (neogeo)
And yes forget N64 lol
Also ScummVM i made a thread about this one for old classic point & click computer games, is a really refined interpeter
http://gbatemp.net/t296461-scummvm-psp
Plugin wise i suggest PSPStatesMenu v0.2 (number 30 on the list here
http://wololo.net/talk/viewtopic.php?f=28&t=7407)
And this little one to download some homebrew app and games
http://gbatemp.net/t292394-homebrew-store-2-5-released
Homebrew games i guess the winner of the Genesis competition should fit, it is Minecraft for PSP and called Lamecraft
http://wololo.net/talk/viewtopic.php?f=26&t=6151
There i tried to help in my humble opinion with the best you can get out of your PSP, so here you go!
EDIT : i forgot to mention one of the best part you also have access to the whole PS1 games library, read this thread for more infos
http://gbatemp.net/t206195-guide-to-conver...1-games-for-psp
ENJOY!!