First thing you need to do. With engine cold fill with water, pressure test cooling system. Look very carefully for any leaks. If you find the leak repair that first. Second thing, Install new t-stat. Fill cooling system, carefully bleed all the air out of system following bleeding proceedure. Run the engine up, if all is ok you are good to go. If not, the next thing to do is a combustion chamber leak test. Hopefully your leak is not the water pump. If it is the water pump, do combustion leak test before wp is replaced. You possibly have a blown head gasket. Your power steering issue sounds like a loose or worn out belt. This is not a cause of overheat condition. Just to be clear. If you have to replace water pump, do not do that until you make sure there is no head gasket issues.
