Welcome to CEG!
New pump and thermostat. (belt OK, right?)
No heat.
Idle fluctuations.
Your coolant level is low. You may or may not have a blown head gasket. May just be a slow leak. Fill the coolant system, you may need to burp it, air in the block will cause no heat and overheating. You may have an obstruction. This is often a piece of the original pump. The expanding air will cause the coolant reservior to rise.
The idle fluxuation may be the intake gaskets starting to fail. Also check the vacuum hose from the UIM to the PCV valve.
