Re: no heat
Several things. Don't just throw parts and money at it and hope it works.
The thermostat should be replaced only if the engine isn't warming up. A t-stat that is stuck open will result in the engine not warming up, evident by the gauge reading very low and as a result you will have no heat. If the gauge is reading normal, replacing a perfectly fine thermostat will not do anything.
There is a valve on the hot water hose leading to the heater core. This valve is vacuum operated. A spring keeps it normally open. When you set the HVAC control for MAX AC or OFF, this valve will close off the flow of hot water. With the HVAC control in some other setting and the engine warmed up, both hoses should be hot. This indicates the valve is working properly and hot water is flowing. If the return hose remains cold, then your valve is stuck closed. Check the vacuum lines and electric connections leading to it for obvious brokenness. A new valve is cheap and easy. If the valve is operating, and coolant is still not flowing, you either are low on coolant or the heater core is clogged.
The blend door under the dash controls the air flow to the heater core. There is an electric servo that operates this door and it is controlled by the temperature knob on the dash. It is accessible through the glove box oriface once your remove the glove box. Check the electrical wiring to make sure it isn't damaged to unplugged. If you are turning the temperature knob and the actuator just sits there looking dumb, it is probably toast and needs to be replaced. Like the valve, it is cheap and easy.