Technically you can do all the same stuff the PC can, just with PSP files only. Be warned that modding for consoles/PSP is much, much, MUCH harder to do than PC. I had to learn how everything worked on the PC before doing my mod for the Xbox and I've got 10+ years experience modding video games. Plus you're much more limited. If you want mods I'd strongly suggest just getting the PC version. It has any character you could ever want, and tons more than could ever be done on PSP or any of the console.
As far as help goes I'm the only active member that knows console mods. There were two other people who understood the console versions well enough to do mods but both have been inactive for years. I'd be willing to do mods for the PSP, but anytime I change any little thing on my PSP ISO it gives me the black screen of death and powers off. It's not worth the time to me.