CTS, Thermostat, Water pump. I would think that is the cost order. You're right though with the thermostat. If it's not circulating, then it could be the thermostat, but it could also be the pump (more likely to leak first before not circulating the coolant mix).
Someone may jump in soon with a way to test the thermostat.
Is there any debris at all in the expansion tank?
If stalling when warm though, I would still look at the CTS first as this controls the engine ignition/mix more directly. The engine is likely to just overheat and cause damage if it were just the thermostat - from limited experience you would notice a lot of steam and a stuck motor.
I'm not sure where the CTS (coolant temp sensor) is on your car. It is normally nearer the top of the engine block, either on it, or on the coolant pipe at a junction on that pipe near the block. I'm pretty sure it is a black sensor, screwed in to the right of the block, near the top.
Another thing to consider is the TDC (top dead centre) sensor. As I understand it, this is only operational once the engine reaches a certain temp, above which it control ignition. Someone jump in quick if I'm wrong please!
You can clean the TDC sensor, which is located just above the clutch bell housing. Search for this on these forums and you will come up with a few useful posts.
Sorry I couldn't be more specific. I may be wrong and it pays to do your research. (I'm not even sure it stands for top dead centre either, but logically it detects it, or something like it.)