Welcome to the site. I think we've been a bit slack by not answering you.ÂÂÂ

1)To check the values look on
www.parkers.co.uk and just compare the prices on autotrader but differentiate between the engine sizes and the turbos to get an accurate price.
2)For problems do a search in the mk4 section or put a thread up in there.
3)I'm not sure how it compares to a focus (I wouldn't buy one

), but a decent leon should not be over looked.
4)Parkers website will tell you the insurance groups
5)I'm no mk4 expert that's for sure, but from what I can gather the 1.8 is a 20v engine but you can get a 1.8t 20v so it's a turbo (best option if possible, 150bhp minimumÂÂÂ

). I'd say stay away from the 2.0 8v GTI as they don't seem to get a good press and they are about 115bhp but are quite heavy so bhp per tonne is very low.