Get the right engine for you, and aircon / OSS or not according to your preference. These things either can't be retrofitted, or they can't be done easily enough to be worth it unless you
really want to. Whatever it is, you want it with as good condition and history as you can get. As long as the mileage isn't
too high, these are more important.
Hopefully you can find the right car in a colour scheme you like, but you'll find the most choice if you like silver exteriors and black interiors. After that, any other spec items it doesn't have can be bought and retrofitted -
@timmus is the resident expert in that field.
The one you've mentioned sounds like the silver one near Slough with the grey accents and wheels, on Facebook. It's been commented on in the Spotted section in our Marketplace -
here and
here.
This brings us back to the question of what's too high mileage? 150k+ is fine on a diesel - they'll do double that if really looked after - and there are 1.4s known over 200k. But it really could be close to the end for an FSI.
If you really want that one, you might consider as a side project also trying to find a low-mileage engine in a crashed car (i.e. hasn't been scrapped for head gasket/death pipe failure). Renew its entire cooling system pipes and housings as they will all be going brittle, as well as the usual cambelt/waterpump. Then you've got it ready if/when the 150k one lets go, from which you can transfer over the inlet manifold and other bits that have been replaced.
But talk in any case
@A2Steve about the ProBoost remapped ECU, which negates all of the long-term causes of FSI problems with the flaps and cooling system, keeping these replaced components closer to 'as-new'..