may i know the reason for the sand bed? to cultivate bacteria or to have a mini refugium system?
i would suggest you use the 2nd compartment to grow macroalgae instead.
try to keep yr sump simple so that it is easier to maintain.
If you have sand bed / a refugium, it will be a permanent fixture.
I read that having a refugium system, the drawback is after 5 years you have to re-setup yr tank again otherwise, it will crash.