well first you are going to have several factors that will come into play. The first thing you need to know is the height and vertical amount of return water, Which will give you your head, this will consist of vertical height, horizontal height, elbows, ball valves etc. Use a Head caculator to determine your total head.
Here is a link of Mag pumps and the head loss:
For example if you go with a mag 12 and have 0 head you will pump 1200 gph
. as your head increases you lose some flow ex. at 0 head 1200gph, at 1' 1200gph, 2' you drop to 1180, 3' 1150
Powerheads will not give you the return you will need gph
Protein skimmer will depend on 1. is it a hob
? or in sump.
Will the return pump on the fuge kill any pods that try to make it back to the main tank?
As for your pods
, I dont think the impeller will kill all of your pods
while being sucked into the return line, I see pods
being spit thru my return every now and then and they seem ok. but that is just my experience
Hope this helps