Best engine/gearbox would be the 4A series.
Suspension could go well with coil overs up front (I have yet to see what good brake upgrades fit the std struts - spose you could use something from Wilwood)
I have a 24mm sway bar up front - it could use a panhard rod out back.
I reckon 15 x 7 would be ample big enough for the 20.
These are just some thoughts and it bears little semblance of what I have currently done to mine.