Different snakes grow at different rates, I think as soon as it cant stretch its body out to full lenght is when you upgrade. For heating you can get a heat mat, or get two large tiles and a heat cord, coil the heat cord around on the bottom of one tile ( the cord needs to be 2cm apart from other parts of the coil) then glue the two tiles together. I dont think I explained this well enough if you want some pictures I could post them up.