I made a smaller sump, 20g, but i had mine set up with the first baffle being under/over/under and the second being opposite. This helps ensure a flow of fresh water from top to bottom with a nice circular current in the middle. It can also help keep larger debris contained in the first chamber. Also, it was a fresh water and I don’t know what a
fowlr is so take this suggestion for what it’s worth!
Good luck let me know how it’s turns out. Mine was a lot easier then expected so don’t be to worried.
Also, I used glass cut to size I needed but after a while I took those out and used black acrylic to keep out algae growth on the walls. You can buy them in sheets and cut it yourself.