To bad about the glass.
You're layout would work.
Any water movement you have have from the pump pushing the water up and gravity filling the void. More will be from the sump as less restriction but you'll get some movement from the ref, plus you have a little head difference working for you as well.
I'm laying mine out very
similiar and it's my project for today so should be able to tell you how it works, at least for me. I do have a problem, being a low max flow, but more do the size of interconnect (1"). Hope your planning something like 2".
On my ro/di have the output going to a Tee, one side is a float valve in the sump, other side to container I use for mixing water. Find the
John Guest valve works well as connects easy to the tubing, HD carries.