IMHO I would only do the bits that are required, no point ripping out plastic and wrecking the fasteners for parts that don't need to come off and spending yet more money on small parts you need to buy new from Ford. With the S1's ive not really got any idea of new parts availabilty, but i'd be careful what you rip out - you don't want to be stuck in the situation that you can't get the connectors/fixings you need to get a part back on.

In my case i stripped my whole interior out finding bugger all rust etc but then temptatioin set in (we all know how it goes) and ive got yet more ideas of new bits i want to add - all adding up to the final bill

HTH