Prepping for a 75gal build

[Mr_Banana_Pants]

I'm currently in the process of acquiring all the necessary parks to begin my new build. I currently have:

Marineland 75gal rr with overflow
Custom 45gal sump with refugium
Theiling roller mat
Skims 123 protein skimmer
Current loop ic led with 2 power heads
2 retrofit dimmable t5 light kits
CO2 scrubbing filter

My next purchase is going to be a return pump and the tunzes osmolator... I'm looking at the ecotech vectra... and my questionso are for everyone, is it better to use the pump externally or submerged to keep it cooler (keep reading they can run hot)? And if I'm planning on using it to feed all my reactors as well as return should I purchase the L1 or does the M1 have enough juice? I'm gonna be pumping about 5ft up.

 

[Mr_Banana_Pants]

Bueller?

 

[Reef2zach]

External pumps will always run cooler water that being said I have 6 submerged pumps in my 75 and never have heat issues