My oh my...
First of all, there is no Loophole, Piracy is piracy.
You can share Homebrew all you want and most Homebrew capable PSP's can also play Backups of games you own.
So lets not talk about that again.So lets have a look at your other questions.
PSP-1000 units (Phat/Classic) are a paradise for Cutom Firmware but they are hard to get.
Most PSP-2000 (Slim) can install Custom Firmware and make bateries but the newest ones cant.
And you are right, on PSP-3000 units you cant install customfirmware at the moment.
There is a Homebrew enabler that works on PSP-3000 (checkenHEN) but it is very beta as far as i am informed.
Have a Look at
THIS THREAD at Dark-Alexs Forum
(he is THE custom firmware and custom firmware installer creator)to read up on the Models.
And at
THIS THREAD on the MaxConsole forum to identify the Packages.
So... you should check if your brothers friends PSP can use
THE OPEN SOURCE PANDORA BATTERY CREATOR to make a pandora battery.
If he can
you dont need to look any further to buy anything else but the PSP for your Brother

his friend can make the Memorystick and the Battery without extra cost and material.
(in my experience like 98% of all memorysticks are compatible
(dont buy lexar memorysticks and if it is too cheap to be true most of the time it isnt
))
so... dont buy a PSP-3000 (at least for now) and look at the box codes or ask for them.
And feel free to ask about anything that is not clear but pirated games...