No, the 6qt is fine for any animal under 500g(even bigger if the snake decides it doesn't want bigger accomodations). Yours is only around 100g, so definitely will be fine in a 6qt.

The flexwatt will not hurt the tub whatsoever as long as you have a quality thermostat controlling it. www.reptilebasics.com you can get both the thermostat and the flexwatt there. Just be sure to tell Rich to solder it for you(you have to buy the wire for it).