I'm in the class that started on March 4th.
The dress for all of ground school is "business casual", that is: no jeans, no tennis shoes and a shirt with collar. Polo/golf shirt and dockers will be fine. Having said that, about half of us wore a suit or at least a shirt and tie on the first day and from the comments of the instructor, I'd say it was appreciated.
You are highly encouraged (if not, required!) to do jump-seat rides for observation purposes prior to starting IOE. The suggested number of rides is 10, but there is nothing stopping you doing more. (Coming from the military without any Part 121 background, I intend to get most of mine done before the sims start). Therefore commuting home at weekends is very much the norm.
The indoc phase lasts 12 working days, hence the Thursday start. You will then be ready to start the aircraft-specific systems phase on a Monday.
Our first impressions of AirTran have been very postive. I think you'll like it here too.
Shag.