Smoking indoors is prohibited in Austin, so you should not have any problems with that.
As far as places to eat, here is a list of good places that I have been to and recommend. Definitely call to make sure they are open on Thanksgiving Day.
Eastside Cafe:
http://www.eastsidecafeaustin.com
Green Pastures:
http://greenpasturesrestaurant.com/ (not my favorite but decent food)
South Congress Cafe:
http://www.southcongresscafe.com/
Olivia:
http://olivia-austin.com/ (I really enjoyed it!)
Vespaio:
http://www.austinvespaio.com/ (was a little disappointed but wasn't bad)
Roaring Fork:
http://www.eddiev.com/