My coops are small 18 and 22 square feet.
I keep the waterer near the people door.
Yes, you fill from the top.
When temperature fluctuates from night to day excessively, water in trough will rise. I check as temperatures rise and tilt to dump excess if needed. GC
I use a Galvanized fount with a heated base inside my well ventilated coops.
I use a hundred foot outdoor extension cord plugged into a WR GFCI outlet.
Outside of coops I use rubber bowls.
GC