Im in the similer boat to the OP but have decided when the time comes to go RS Turbo engine route.

N/A Zetec (excluding tb's) would get dull after a while, lets face it, its only going to be on a par with majority of modern day cars at best anyway. If your not going to mod at all then Zetec would be best i think.

If you decided to turbo not sure if its best to fit the zetec then turbo it or fit the rst lump and zetec bottom end that?

Suspension wise unless you go Spax non adjustables (£280) it appears to be a straight jump up to big money. Likes of Koni's are 100 notes a corner excluding springs