You'd be far better off using a FRS exhaust (log) manifold. It is after all designed to both fit the zetec head and the Focus engine bay. There are still plenty around, and cheap, and not cracked like many ERST ones.

As said, unless you want to just run a track car, you have to retain the EEC-V to run all the ancillary electrics from alternator through to the instrument cluster. Take out the MIL bulb and use a V3 Megasquirt to run the engine.

The standard inlet manifold (and TB) is fine if its the single piece moulding (>2003), its what the FRS used. Don't know about later (multi part) ones. FRS injectors come up for sale every now and then (42lb) and obviously work. You'll need (ideally) an uprated (or FRS spec) intank fuel pump, have to drop the fuel tank for that as the Focus doesn't have an access hatch.

What are you going to do about a 220mm/IB5/hydraulic clutch?

Martin