In order to stay with the "simple" plumbing" plan I suggest a "submersable" return pump rather than bulkheads (cost) and external pump ...for the sump...
A Mag 12 with 1 1/4" line...coming OTT (over the top for antisiphon effect) will give you 1037 gph to the tank...
Right where we want to be...
Let's go back to the sump...and review...
We got the water "down" to the sump through the Overflow...
It goes past/through the Skimmer and does it's "thing" (protien fractionalization) and then we need to get it back "Up" to the tank...
This is where the "Return Pump" comes in...
There are many makes and models and "sizes", but really only two "types" we need to think about...
Either a "Submersable" pump..one that sits "IN" the sump.."IN" the water and pumps directly to the tank..
Or an "External" pump that sits "Outside" the sump and is fed through a bulkhead in the side of the sump...to pump...and then to the tank...
As both types of pumps come in a varity of sizes, it's not so much "Which one pumps more water?" as it is in "How" they do it...
The External because it sits "outside" the tank is generally thought to transfer "less" heat to the tank because the motor is exposed to air for cooling (some have fans)...and can sometimes be easier to work on being more "exposed"...
Although they can sometimes be "noisier" as well...
The Submersible pump sits "In" the water and runs quite a bit quieter because of that, although the motor is sitting in the water and can/does transfer a bit of heat...as well as being a bit messier to work on...
Now Both typs have their "exceptions" some Externals are quiet and some transfer a lot of heat...and some Submersibles run cool but can also "rattle and vibrate and drive you nuts...
As the Submersibles are "generally" cheaper and much easier to hook up (this is plumbing 101..
) as well as quieter, I "suggested" a Mag Drive pump as the choice for this installation...
As our "Goal Flow" from/to the sump is to be ~1000 gph (gallons per hour) I "suggested" the Mag 12 as it will pump right around 1037 gph - 5' head through 1 1/4" line....
Right where we want to be...for our "Goal"...
I'll get to "Head" and "line size" and how they affect flow next...