I'm doing a similar thing just now, Puma lump into a base model mk5.

I bought a complete and driving 1700 Puma for £250 so I have everything to do the conversion plus alloys etc, so its a cheap way to more power. There is a comprehensive guide on www.zsoc.co.uk to the conversion and they are all very helpful on there.

The wiring sounds pretty straightforward, as you basically trasfer the engine loom + ECU from Puma straight over to Fiesta and all plugs in as it should

Best of luck whatever you do