What power are you after? that really dictates gearbox/fuel pump/injector choice....

As for exhausts, there are 'custom'/off the shelf manifolds available, don't see why the mk1 rs foci manifold wouldn't fit or you can use your rs turbo manifold and re drill/tap the zetec head. The latter should leave your exhaust free to bolt up as normal (roughly??)

I personally would be happy with whatever ford pressure reg is on the fuel rail the zetec lump comes with, most things that use Bosch injectors are 3bar any who. You will need to use your rst cross over pipe, more seem to use backwards fiesta rst crossover.

You need to modify the engine mount as per zvh i believe and use a 1.8zetec sump... then you need to sort out an oil return for the turbo.

Injectors are really chosen by what power you expect/want.... Your turbo for instance (If its a proper stage 3) should be good for 270-300 brake,

Obviously you need some kind of management, i (again personal choice) would go megasquirt but if your not keen on diy set-ups then omex/gotech/pectel t2/cosworth etcetc are all good candidates.

Again this is mostly opinion, i would choose to go mtx75 (or find a focus rs box) whilst the engine is out etc if you are after much more than 220brake as the zetec WILL have a lot more lo end torque.

Im not the best person to give advice on this, as i haven't done it...... but loads have on here.

Good luck!

Rob,