Kerep an eye on the engine temp. Its suppose to run rather hot by design with a 195*F themostat.
As long as the coolant system can retain its pressure as controlled by the radiator cap, say 15-17 lbs, it will be fine. When the coolant system boils over into the reservior, the there is a problem. At least this is what the dealer told me on my truck.
By design, the engine temp should run on the thermostat. This can be anywhere from 190*F to 205*F. As long as the system can retain pressure and no coolant is added to the reservior when cold, you should be good to go. The top radiator hose will be tight when you try to squeeze it with a rag.
The belt issue should be okay. Belts do stretch in time. Like I suggested earlier, a dragging accessory will help the stretching process.The water pump has a flat pulley on it and one will not hear it slip when the belt is stretched too far. If the backside, the non-grooved side, is very glazed, then one can bet the w/pump is slipping. Hopefully, the rebuilder did not put a standard rotation water pump in place of the reverse rotation water pump. Then the engine would overheat and boil out all the time.
You might try and clean out from the rear, the A/C condensor and radiator to clean out the debris to help air flow through both items. You would be amazed as to what and how much falls out. Spray both sides of the radiator and A/C condensor with 409 or Simple Green and let soak, then rinse with the garden hose.
If the engine was rebuilt, the radiator, themostat, cap, hoses, coolant and belt should have been changed also. The system is only as strong as its weakest link.