[iedwardsIII]

Well, there isn't any problem with playing PS1 games on a Slim so you don't have to worry about that. The only thing that's difference between the fat and slim PSPs is that
1) some of the old ancient homebrew (that you definitely won't use anyway) can only be used on the fat and
2) the weight difference.

And a 4GB pro duo is okay but nowadays a lot of us have 8GBs. The game ISOs, emulators, roms, and music take up a ton of space. But the two things you need to go to custom firmware are a magic memory stick (mms) and a pandora battery. And since magic memory sticks have to be between 512MB and 4GB then I guess you have to choose whether you're going to get two memory sticks and have one of them be your mms and the other be your main memory stick. Or the other route where you just have one and if it's that case then you're going to have to only get the 4GB.

And Klause isn't scamming you, the PSP he has already has everything you want so unless you're dying to hack it yourself you might want to consider his offer. But if you do decide to mod it yourself read the guide in my signature carefully because as I've read on this site frequently from people who try to mod to fast, it's really easy to fry your battery, so just open it up slowly.