You won't be able to use a DS screen at all (they're specially designed for the DS, have a weird resolution and cannot support analogue composite input without a conversion board). However, you can get away with using a stock LCD and driver board, the kind they usually put into rear-view camera disp...

You can run pcsx_rearmed without X without having to compile it differently:

xinit /home/pi/pcsx_rearmed/pcsx $* -- :0

It will open on display 0, but you can change the display by changing that last number. Make sure you CD into your pcsx directory before running to load all your settings/bios.