If I where you. I would move you post to DIY, Equipment and Lighting forum.
There are alot of plumping experts there. And give you great advice there.
Here's the basic overview of the tank you have.
The tank circulates and overflows into the drain. Then gravity takes over and flows into the sump, via tubing or pipe. The water travels through the sump and gets pumped back into the tank via the return line via tubing or pipe. The return line goes back to the top of the tank. In my experience typical overflow holes is 1" and the return holes is 3/4 inch.
The information/questions will be more advanced as things progress. Just ask.