If the thermostat wasn't opening it would *REALLY* overheat when you are driving it around harder. If the coolant flow was obstructed by anything else (clogged radiator, clogged distribution tube, stuck thermostat, pinched hoses) then it's going to overheat only a little at idle and a lot when the motor is working harder. If it doesn't overheat when you are going down the road at 65 mph then it simply isn't a coolant flow issue.

It's possible you have a cheap sort of water pump that doesn't pump effectively (AKA not at all) at idle speeds, but finally starts churning the water the way it should when revved up. Again, if it wasn't pumping well at all the overheating would be most acute when driving at speed, when the motor is putting out 10 times more heat. I've never seen such a pump, but it's possible, or maybe your idle speed is unusually low?

I'd fiddle with that electric fan and get it working first, I suspect all your issues will go away.
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'63 PV544 rat rod, '93 Classic 245 + turbo