Josh,
Welcome to TFP.. you will love it here...
I'll get us started, but I'm sure others will follow soon.
I can't see your valves very clearly in your pics, but generally, there are three basic configurations that your Pool and Spa can be in:
1. Pool mode.. this is where the valves are set so that the pump sucks water from your skimmer and/or main drain into the pump, through the filter and heater and then via another valve back into the pool.
2. Spa mode.. this is where the valves are set so that the pump sucks water from your Spa's drain into the pump, through the filter and heater and then via another valve back into the Spa.
3. Spillover mode.. this is where the valves are set so that the pump sucks water from your skimmer and/or main drain into the pump, through the filter and heater and then via another valve back into the Spa. In this mode, you put water in the Spa which has no where to go but to overflow into the pool.
I suggest you play with the valves so that you can duplicate the above conditions.
How do you plan on keeping your pool chlorinated?
I don't have a Spa or heater so I'll let others step in with some ideas on your heater issue.
Thanks,
Jim R.