Not handy, but the water level in the sump should be a bit below your filter socks. You don't want water flowing over the filters socks into the tank, so the water level is maybe 1" below that. Look at the area where you skimmer drains into your return section. You don't want the water going OVER that last baffle, it goes under. The reason is to prevent bubbles entering the tank, so the water level is just below that final baffle (with the sponge), so water travels thru the sponge (not over).
In the overflow, you emergency drain is the one in the middle with just an empty open pipe. The water level should be ~ 1/4" below. Water can be slightly flowing in, you balance that more for noise that anything else. Water flowing into the emergency will make noise (alerting you to a blocked primary), so you adjust the level so everything is silent.