I don't think you'll be likely to have a panic attack. I've never known anyone to have one, and I know quite a few people who smoke. If you do find yourself feeling anxious, try putting a film on to distract you and get some food as well.

The first time I smoked I got a little bit high. I didn't smoke too much though, because it was a friend's stuff we were smoking. I didn't feel any bad effects; possibly because we didn't smoke that much, possibly because I was with friends, but probably because it just wasn't likely to happen anyway.

As for how much, well take it slowly, and just see how you feel.