I have an Alita 60 and love it. Like I said, it's loud- but put the load on and it will quiet instantly.
A manifold is just a long tube. No reason in my mind why you would have to have a loop. Many people do that to run it around the perimeter of the fish room so they can tap into it at any time, that's all. No biggie.
Oh, and when I put my pvc together for my side of the rack, I didn't use any glue,and it holds tight just fine. No blow out. I *did* use a rubber mallet to make sure it was in tight, but wanted to be able to disassemble if later if I needed to make an mods or just take it down.