Good to see another potential owner joining the fold!
Engine wise they are pretty bullet proof, very understressed strong BMW engines that usually have no issues, oil leaks on perished gaskets are worth looking out for (but don't usually cause major issues) and sump damage is the big one as already mentioned.
Car wise you have a few options depending on your preference and budget..
Series 1 cars tend to feel more direct owing to the race inspired suspension setup, many say that these are the best for a country lane blast and track driving - but are less comfortable on longer journeys. I am 6ft 5 and have no issues but you would have more space and less NVH in a later car. Although this can vary massively car to car, so drive a few before making any decisions.
S2 bridges the gap to the S3 and is starting to go down the GT route as it was americanised, and I would say I have heard from S3 onwards they are more comfortable and feel more GT based through each model than its predecessor, that being said I have driven an S5 and I was expecting it to feel vastly different from my S1, and it didn't - it felt very very similar and is very much a case of evolution not revolution.
In summary Series 1 cars are the best value for money, but a Series 3/4 will be slightly more practical.
For some the S1/S2 lights are the original and best, others hate them and so its S3/S4 or nothing.
It comes down to price, and whether you want the original concept and the most raw experience, or a bit more comfort, space and toys. All are great cars, and you won't regret purchasing one - although once you do there is the question of sidepipes or a rear sports exhaust, and that is a whole new can of worms..
