The thermometer should be left on all the time so you can keep track of the temperature & make sure it's good to go. Thermostat should also always be plugged in & working, though it may not always have the lamp on. So you're going to need to use those 24/7 no matter what. It's the lamp & bulb that might not always be on, depending on the temperature.
I'd at least get the 8.5" lamp so it can spread the heat out a bit more. You shouldn't need more than 100 watts for the lamp since a bin is pretty closed in & should hold heat well.
However, you've mentioned wanting to use a C&C cage during the summer, so it may be a good idea to get a 10" lamp anyway so that it can be used in the summer too, just in case. Even so, you might need two 10" lamps for the summer cage if you make it 2x3 or larger. It'd be a good idea to get the 1000-watt thermostat as a "Just in case" for that possibility - it has three outlets, so it control that many lamps. The 500-watt one is a bit cheaper, but only controls one lamp, so you'd be out of luck if you find you need a second lamp for the larger cage.
~*~*~ Kelsey ~*~*~
RIP my sweet Lily ~ 6/12/08 - 1/20/12