Hello there mate. Welcome to the forum.
Alternator loom is an easy one to do. If its the three wire loom you're referring to then its just plugging it in. Although the alternator side is a bit fiddly.
Airbox is a straight swap from a mk1 focus 1.8 or 2.0 petrol. Don't get one from an ST170 as the hole in the bottom is triangular. You want the round hole so you can attach an air feed.
Remap- vantuner (MARTYNX on the forum) is your man for that. Loads of people have had remaps by him and are over the moon with them.
Decat has been covered on the forum. Best bet is to hack out the innards so it still looks like there's a car there

Front end- do you mean the new curvy shape one where the bumper swoops up to the grill or the 2006 shape which hasn't got the square boobs on?