Oh there will be plenty of places to try your hand at acting. I'm sure there will be student drama clubs in any of the unis you are looking at. I know that both Edinburgh and Glasgow have rather a lot of theatres. Not so sure about St. Andrews.

I doubt there will be much you're looking for that both Glasgow and Edinburgh wont have on offer. They are both huge, busy cities with lots to do.

It is so hard to try and be unbiased when it comes to talking about Glasgow. I just love it soso much. xD