Return To Sender; AKA Return Line Help

I'm planning the return lines for my 113 gallon.

I'm doing a BeAn Animal overflow but only a partial C2C overflow due to the side eurobracing.
I'll have 2 returns, one on each side of the overflow box, and I plan to "Y" that once in the tank using Loc-Line.

I'm planning on 3/4" return plumbing, should I stick with 3/4" Lock-Line or reduce it to 1/2"?

Does the "Y" from the return line reduce the gph of the return pump (like a 90 elbow does) and does each of the 90 degree elbows @ the bulkheads reduce the gph by 100gph each (for a total reduction of 200gph)?

 

Bump....need some answers please.