Plumbing Question for a 125g aga dual overflow

Hey there! im really hoping you can help me, its probably a silly question but I cant find the answer, I am setting up a new system from scratch for the first time (my current setup was up for 5+ years) and I have a question about the return line.



my setup is

125g AGA Dual overflow

aheim 1262 return pump with a 3/4" ID return line fitting on top
ruby 36 sump that has two 1" drain lines. flows from left to right,[return/skimmer->refugium->return]



based on what I have read it seems that for 600gph the return line needs to be 3/4. My overflow kit claims that the return line bulkhead is 3/4" but its 5/8" ID. Now I plan to run just one pump, Teed off to feed both sides with built in gate/ball valves to adjust flow, and also a T closer to the pump to feed water back into the refugium also being adjusted by a gate valve to tune the flow, I know sometimes refugiums cant keep up with the flow in the sump to do what they need to do.



Should I get a larger return line Bulkhead?

should I run a larger ID pvc that Tees off to a smaller ID pvc to each side?



also my drains are 1" ID



im open to any suggestions! thanks in advance!! =)