I would take a temperature reading of the driver side rad tank with an infrared gun. That will tell you if your gauge is reading right. If temp of rad tank is under 200-210, I would think your gauge sender is faulty, time for a new one.
The coolant tank going down could be you don't have the cooling system filled all the way. I would open rad cap, start car and let it warm up. Watch for coolant flowing through the cores into the end tank (this means thermostat is open) and then slowly add coolant to fill rad. When full, put cap back on (engine still running) and let run for a couple more minutes (you can check the surface temp on rad tank now). Then shut down engine. Let it cool down and top up the overflow tank.
If a blown head gasket, you would either see white smoke out tailpipe or chocolate milk in oil pan.
For the e-fans you should be able to manually short the fans into operating. Also with above filling/temp test, fans should start and operate at their set temps.