Get one where theres still plenty of parts for it. i think loads of parts are available for the mk3 and mk4 escorts etc.
MK1&2 fiestas do have a fair few parts come up on ebay and hadrians panels still make there wings, sills and floorpans etc so that should be okay to start off with.
But it does get pricey fairly quickly, but you can infinatley customise and modify it as you go

Edit: i'll add you on ps3 later