My system is overheating. If I set the thread count to 0, does this mean it is not using any CPU and only using the GPU?

If you'll set "Number of threads" to 1 (it's minimum value) then our software will not use CPU threads at all, only GPU ones. However, at least one CPU thread will be running for each GPU. It won't do any "heavy" work, just syncing data with GPU but this CPU core load level can easily be 100% even in such simple case.

Overall, you're really need a good cooling system if you're planning to run our software 24/7. Otherwise you'll face overheating problems. Sooner or later.