I'd advise you to buy a TT6 from the start. It'll be cheaper (I don't know what average prices are in Italy but this is true for UK market prices). You can then replace what needs replacing, when it needs replacing.
As for having a zero miles car, I don't think that's right. The chassis, body panels, suspension components etc will still be 20+ years old. You mentioned a Getrag for 5k: presumably that's a 2nd hand part that's 20+ years old and has done lots of miles already. The same goes for engine, diff, etc, unless you buy everything new, which would be really really expensive!