I prefer big bumpers, some people say they can hide rot etc but I've yet to
find a car with horrific rot to the bottom of the rear panel or wing
bottoms, and at the end of the day neither is a major issue. The sills are
fairly hidden, but you can still see them. It's also worth noting that with
the introduction of big bumpers (1990) the electrics system was modernised,
and is basically the same as fitted to the MK3. This makes things like
engine swaps from MK3s much easier, but also makes buying things like
replacement clocks hard work as they were only produced for 2 years. 88 and
89 cars have the big windows in the front doors, but shouldn't have big
bumper kits if being sold as original.

Obviously the newer the car is, the less time they've had to rot - IME major
areas for this are the bottoms of the A pillars (hidden underneath the wings
and not able to be looked at from underneath either). You need to take the
wing off to check properly, but if you can see a hole in the inner wing in
the rain tray (where the blower intake is) at either side, then there'll be
a hole big enough to put your fist into in the box section on the other
side. Other areas are door bottoms (tends to rot where the skin folds over -
presumably not well seam sealed) which need replacement doors if you want it
perfect, door handle apetures tend to get screwdrivered by theives and rust.
Tailgates get dirty and rust, and aren't cheap to come by, and replacement
black stickers for around the window run to about £30. Other than that,
they're pretty solid. Certainly well ahead of other cars of their time, and
a lot of far newer stuff like Fords...

As for wheels, 8Vs should really be on steels, 16Vs pre 1990 should be on
bottle tops (Montreals) and the post 1990 16Vs can be on BBS RAs, which are
worth £400 a set in good nick, £150 a set if ropey.

That's about it off the top of my head. Have a google for matey matey as
they've got a buying guide.