Hard plumbing advise for 120g

[Greybeard]

YOUR LOOKING AT IT UPSIDE DOWN. 1 PUMP, THRU MANIFOLD, THEN SPLIT INTO THE TANK

Ah. Makes more sense now

I have a similar design, without the manifold. From experience, I can suggest a bit of large diameter silicone hose between the pump and the hard return lines. Helps to isolate pump vibration. Here's a view of mine, before it got buried under other equipment. You can just see the 1" silicone from the pump, past the skimmer... 1" pipe across the back, 2x 3/4" pipes through union ball valves, back to the tank. Works great, easy to adjust, doesn't make any noise.