I'm currently putting a system into a Celica myself (a '99 UK GT, so same shape as yours). I've got an EPIA M10000, Opus PSU, 120Gb HDD crammed into the glovebox, it all runs very well.
Just been finishing off the screen install, a friend of mine has blended a lilliput into the centre console for me... we've removed the hatch, shifted my single DIN stereo down into the bottom of the double din opening and then moulded the touchscreen into the space that's left. It's gonna look good, I think, when the screen bloody well starts working again
If you've got any q's just give me a pm.
Interesting that you don't like touchscreens... I did experiment with a couple of solutions before I went with a touchscreen (remote control, touchpad, numpad), but they were all just too difficult when you're driving. I've found that after a bit of practise the touchscreen becomes second nature and you barely have to take your eyes off the road to use it.