Be sure to get the exact temperature thermostat for your engine. Mine was 192 degrees F. I like to use a small amount of high temperature silicone to seal the gasket surfaces on both sides of the thermostat housing. Be sure to point the thermostat in the correct direction too.
Check the hoses and if they are bulging or swollen replace them. I always put a small amount of grease inside the hose to make it slide on more easily.
As far as refilling goes. Here's what I do. I mix the coolant 50/50 with water before pouring it into the radiator. I fill the radiator to the top and fill the coolant reservior to the cold fill line. I start the engine and run it to operating temperature, keep it there for a few minutes to insure the thermostat has opened up and the water is circulating in the system. Let the engine cool down for a few hours, then refill the coolant reservoir to the proper level.
Caution: Don't open the radiator cap after filling the radiator and starting the engine. The water will just come back out due to pressure and expansion. If you plan on opening the radiator cap....be sure the engine is completely cold.
Hope this helps ! Good luck