I used to wear cotton vest and cycling-type shorts - it doesn't really matter if you are wet, as this will help to cool you down and you won't really notice whilst you're doing it. As much skin as you can show the better though IMO.
I've been practicing for a long time on and off and have never been told not to wear cotton, I have these shorts and these vests amongst other things from the same company, bargainous in the sale.
Any legging and tee shirt will do while you are deciding if it is for you. Try to avoid tracksuit bottoms though as lots of the postures involve compression and all excess fabric will just get in the way.
Don't worry to much about what you are going to look like as you will be running sweat and purple, it's not really possible to look stylish.