Creating a Sump From a 55 gal tank

Hello and thanks for taking the time to read this.

I am in the process of setting up my 125 gallon fish tank (with overflow, drilled in the center) and need help with ideas with what will be the best set-up for my tank/sump area. Please understand that once I put the fish tank on the stand that I can-not remove the sump. Heck once I put the protein skimmer into the sump I barely have enough room to remove the lid and cannot remove the skimmer without moving the entire fish tank, thats how big it is (I believe it's a ASM G-3).

Coming from the center of the tank will be 2, 3in PVC pipes and would like to know what/where is the best placement to put the pipes in the sump.
I plan on placing baffles in the 55 gallon sump though I will do that once I read up more on it. Attached is a basic picture of how it currently looks.

Thoughts/advise?

 

Are the water lines already drilled? Why 3" lines? That's really big.

 

Yes the hole is drilled in the tank, I was thinking maybe going to Lowes/Homedepot to buy a fitting to reduce the size however before spending any money, I wanted to see what others thought.

TY