asking a stupid question but need to know

Man, what a stupid question. Just kidding.

The coolant level in these cars is checked at the reservoir. It should be full when the motor is cold. That's all you need to worry about.

My sud runs at 70 degrees (according to the in car gauge, anyway) and the fan cuts in when it reaches about 80.

Typically it should read 80 degrees when warm and stay there, but this depends on your gauge. Just watch the spot where it doesnt move around much after driving for some time. On cooler days mine tends to hit 80 then sit just under for the whole day and I never hear the fan come on, but on warmer days it sits slightly above 80, especially in traffic and the fan comes on.
As for coolant level, I always fill my tank to about 3/4 full, leave a bit of room for expansion and you should be fine. It will drop over time as some evaporates or if your tank leaks along its seams, which is common.