1.8T or 2.0? depends what you want, if your after a car to get from A-B then go for the 2.0, if you want something a little bit faster and with a huge amount of tuning potential go for the 1.8T, they are both reliable but I guess on the 2.0 you won't have a turbo to replace if it went wrong (I had a 1.8T engine do 135,000 miles and the turbo was still on it's first turbo though)
Things to look out for? I've not long had mine so not sure! check all the usual, service history, blue smoke, fluid levels, break wear... blah blah blah.
Apparently the electric window runners can go, so test the windows and try closing the doors and lisening for any rattles with the windows down.
Have a seach on the forum, im sure this must have been asked lots of times.