My heater will not blow hot air slightly warm.

With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are both hot, the heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.

One step at a time. Do the other checks and we'll go from there.

That's indicating a plugged up heater core, probably from old dexcool getting sludged up.

You can remove the heater hoses and try to flush the core with water pressure from a garden hose but if the engine is dirty too, it will get plugged up again quickly.

It's going to take some chemicals and professional flushing to get the rest of the cooling system clean and even then it may not come clean because it's just too crusty.