Hi Mate, wise choice on looking for a sprint
Replacement wings for the Sprint are harder to come by than for Suds, which aren't that easy! Forget about popping down to the local Motor Factors, they can't help. This site in Germany were very helpful to me recently and is one of the best/easiest source of new parts
There are a couple of guys that can supply second-hand parts
Welcome to Justsuds
Justsuds are pretty good, Mr Sud up in the North East also preety good.
As for what to look for, then RUST! Check the areas around the rear windows and on the rear pillars under the hatch where the telescopic arms sit, the obvious areas under the sills, jacking points, floors, front suspension arms can rot where they join near the hubs, inner wing rails, area around the windscreen bottom, boot floor etc etc. A good history file is sometimes a pointer to if a car has been cherished or not, enthusiasts tend to keep every bit of paperwork
But all that doesn't matter, once you have heard that boxer sound and driven it you will buy it, you have no other choice, you just don't know it yet
Heart will win over head 99% of the time, it's only that 1% when the Mrs is with you that changes things