Too full will make it over flow, Rusty is right, fix temp gage not hard to troubleshoot, or possible by temp,oil press,amp gages, you got lots of choices, could just be the sending unit, maybe it isn't even plugged in.
No fan helps after 50 mph. Stay with 190-180 thermostat. Your not hot till you get onto the 220-230 range. Make sure you use antifreeze and at lease a 10+12 lb cap on the radiator.
was just on the site looks like 22.99 http://www.flowkoolerwaterpumps.com/store/Thermostats/c22/index.html
Looks available to me I have one in my cart.
That wont hurt anything and should run good there, everything being new generates a little more heat, I always go by 220 or under is ok. Too cold they dont get warm enought inside and thats no good either.