If you're having trouble with heat, go with the 11" flexwatt. It is not adhesive, but I've found no need to do so with it. You can use foil tape I believe it is.

A 10 gallon tank will be fine for awhile.. up until he's around 2'. you may even consider moving the snake to a smaller (and more secure feeling) rubbermaid/sterilite shoebox type enclosure for now. Especially if your snake isn't eating, this can help.

The best thermostats are generally held to be Helix.. but they are pricey. Whatever you get, go with a proportional thermostat, not an on-off, as these can let the flexwatt overheat. Personally, if you are on a tight budget, I'd recommend going to the hardware store and getting a rotary lamp dimmer and a 6' extention cord and wiring this up to the flexwatt.