Things like suspension components and bushes are still readily available, and affordable. Plenty of other mk4 parts (a pillar seals!) cost more than you'd get for both your kidneys if and when you can find them. If you want to keep it original, then it will be significantly more difficult. Original backboxes for example are very hard to source, but an aftermarket mongoose for example would be a fair bit easier. Same with bushes, you can get poly kits from a large number of polybush providers that cover the entire car, but if you wanted to find genuine Ford everything, some bushes will prove far more problematic to source.

You have to remember the youngest are 30yrs old so again be realistic with expectations on things like service history. I'm positive there will be people with full historys out there, but equally a hell of alot of people will just be doing their own servicing. Buying a classic is very different to buying something off a forecourt, but thats why forums like this exist - to get peoples thoughts and experiences and hopefully help you avoid getting stung