I'm on a similar endeavour: I'm going to use a 1.6 Ecoboost in my kitcar I'm building.
I will try to get away from the aftermarket ECU (around £2k) and work on the standard ECU to be bought from eBay + loom (down to £400). The difference of cost makes the challenge worthy!
Points of interest I so far got acquainted to:
1. the ECU will need the keyless transponder to work (It seems Fiesta ST 1.6 came only with keyless option as my wiring diagram doesn't show the wiring for normal ignition key). If you get one of the eBay's set, that would work.
2. It seems there is no need for the body controller box. Just seems...
Where am I now?
1. I have the engine on the swivel with me looking at it thinking "where shall I start with?".
2. Preparing myself to start the basic work: timing belt, water pump, crankshaft seals, clutch, and maybe flywheel.
3. looking for a gearbox to mate with it. I dont want to use the 6-speed ST one.
Cheers.