Hard to start at times and stalls at idle

There are two things to consider. The first is your observation the engine does not run smoothly. That is either due to misfires or idle speed that is too low. None of the parts you listed will cause this. Also, one of the important sensors is in the distributor. When it fails, the engine will not start at all. The fact the engine will eventually start indicates all the parts in the fuel supply and ignition systems are working.

For rough running, the spark plugs and wires are the best suspect. Next is to look at idle speed. If the battery was recently disconnected or run drained, the engine computer will have lost its memory. Most of the data will be relearned automatically, except for "minimum throttle". Until that is relearned, idle speed will be so low, the engine may not start unless you hold the accelerator pedal down 1/4", you will not get the nice idle flare-up to 1500 rpm at start-up, and it will tend to stall at stop signs.

To meet the conditions for minimum throttle to be relearned, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

Idle speed is not adjustable. It is computer-controlled on fuel injected engines. Reread the last two paragraphs in my first reply.

The throttle position sensor has no affect on idle speed. Its readings simply tell the engine computer throttle position, direction of change, rate of change, when your foot is off the accelerator pedal, and wide-open-throttle. When your foot is off the accelerator pedal is when the computer must be in control of idle speed, but it does not know that until minimum throttle has been learned. When that is learned, it puts the throttle position sensor's signal voltage in memory. From then on, anytime it sees that same voltage, it will look at other sensor data to know how to control idle speed.

The coolant had to go somewhere. Given the additional symptom of running hotter than normal, a good suspect is a leaking cylinder head gasket. Coolant can go into a cylinder, then out the tail pipe as white smoke, and combustion gases can go into the cooling system. If those gases pool under the thermostat, that can prevent it from opening. Thermostats must be hit with hot liquid to open. Hot air will not do it.

There are two tests to consider. The first is a chemical test at the radiator. While the engine is running, air is drawn through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow. You may be able to borrow this tester from an auto parts store that rents or borrows tools, but they will make you buy your own bottle of fluid. That is because it becomes ineffective if it freezes or if it becomes contaminated with coolant. They do not want to risk borrowing it to the next person with contaminated fluid. This test just takes a few minutes, so it might be less expensive to have your mechanic do it.

The second test is simply to add a small bottle of dark purple dye to the coolant to check for where it is going. Search a day or two later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If a head gasket is leaking, you will find the dye inside the tail pipe.