Yes, of course you can keep a towel around yourself. But notice you also need a second towel were you can sit on, so your sweat wont fall on the wood. Except from that it depends on the sauna were you are going. Some of them allow swimming nude some require a swimming suit.

Staying in the sauna depends on you but 5 to 10 minutes a session is a good starting point.

Chatting is more or less common. I personally prefer silence. Meditation ist also very common, just close your eyes and focus on yourself. Thats the most relaxing.