1. i don't want to use it primarily for playing games, but to experiment with it. are hardware mods necessary to execute own code?
As far as I know there are no psp emulators that you can run without having a psp. So you need the console to run any homebrew games.
I can not answer the other questions, as I do not know alot about the psp, but I do know a toolchain that helps alot with developping (also for the NDS (which I use it for), GBA and wii):
devkitpro. And here (which you may already found out) are the main psp dev forums:
http://forums.ps2dev.org/viewforum.php?f=14In #dsdev channel at irc.blitzed.org are many people who know alot about the psp, ds, gba, wii and probably alot more, as well the home chatroom of the developper of devkitpro
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