There aren't many 2.3's for sale second hane infact they very rarely come up, the 2.0 come for sale all the time, i'd suggest getting a low milage one from a mk3 mondeo due to the fact that they come with a mtx-75 box aswell (or at least the correct bellhousing)

Tuning wise i'd be inclined to go forced induction i.e super or turbocharged but there's always the throttle body route if your serious about the track - they do bolt on kits now with throttleboidies that'll see you straight over 200bhp

I think it'd be a good idea but why the focus? Why not go for a small lighter fiesta?

Oh and good luck!