keep it simple and it will be reliable.

id do like this because you will always want more.

2.0l blacktop engine

forged pistons and steel rods with a comp ratio of around 8-1.

bog standard head and cams but with some uprated valve springs

standard head bolts and gaskets pulleys and flywheel

standard sump

you could keep the standard focus/ mondeo inlet to a point or fit a better one

custom exhaust manifold

turbo of your choice but id go for a t34 there cheap and good upto 380hp

with it being a fiesta fit a swirle pot in the boot use the in tank pump to feed it then a 044 pump to the fuel rail.

injectors id go for vxr ones good for 350hp and there only about £80 new.(bigger if you want more power)

gearbox

id use a focus rs box with atb diff

clutch id use the focus rs one

custom shafts

management of your choice.