Sounds like an interesting project, there was a 5 door RSi going around on ebay a while back so why not an estate not many mk3 estates around in good nick anymore either

I think your best bet if you want to make a close replica is to get hold of a crash damaged/rotten RSi complete with all the parts you need (theres a write off on ebay at the moment for example)

It would work out easier and cheaper in the long run than buying individual parts