Would love to see your current plumbing setup. I am starting to setup a 350 myself and your post has helped me already.
So now, for where we stand today haha. At the beginning of the year I just came increasingly frustrated at the layout of the original sump, plus there was extra space that could have been utilized for more sump area. I really like Trigger Systems stuff. You can see I've had their Emerald line 10 gallon ATO container for a couple of years now. So I got looking and the only sumps they produced regularly that would fit in were the 26 or the cube. Cube being too small, and the 26 coming in slightly smaller than necessary. So I contacted Trigger, told them I was wanting basically the 26 custom extended in each direction. For not much more than what the 26 was going for, I got a sump that is a perfect fit into the compartment.
I also got ahold of Red Sea America and ordered a set of pipes to keep on hand. When I did this change over, after only a year, the plastic on the original ones where the flange is by the threads was so brittle they simply snapped while I was taking them out. Luckily they're great down there and I had replacements plus more for future needs within a couple of days.
The whole 1" pipe inside of the factory Red Sea ones has been the best thing I have found about adapting this plumbing. The tanks are great, but I wish the return plumbing was larger. I lose 50% of my flow of where I'd be at with 1.25" pipe because of the small diameter going through the return. While I love this tank, my next will definitely be completely externally plumbed with that size.
All in all I'm happy where I stand with the current setup. I keep going through circulation pumps in the tank now. Wanting to play around with everything. I started with MP40s, tried both Gyre 210s and 230s with their advanced controllers, and the Neptune WAVs. They're all great pumps. I really wanted the WAVs to work out, but they are a loooooooooooot of pump. I will hang on to those for my next larger tank, but the Gyres are up for sale!
I also bought a 170 stand to set next to this stand and place all my electronics clutter in. Worked out rather well and gave some extra storage.