Building a reactor manifold: question

I'm going to use one sumbersible pump connected to a manifold to run water to all my reactors.

I need to replace these reactor pumps:

1. MJ 1200 295 gph (powerhead flow rate) / 1300 gph (circulation flow rate)

2. MJ 1200

3. Mag5

4. Eheim 1250



Q1: On the MJ1200, what is the difference between 'powerhead flow rate' and 'circulation flow rate' ? I assume that I am using them as powerheads since they are used with my CaRx and GFORx.....



I presume I need to replace about 1400 gph (which is the total of all the pumps listed, consideing powerhead flow rate).

Q2: How big of a pump should I buy for the manifold? I assume 1400 gph minimum, but should I go much bigger than that? (looking at Mag18)