Hi,
Fot second compartment, you might want to put your sand in a container or go without the sand, just cheato. The sand might restrict the water flow over period of time. You might also want to simulate a power failure to check for any overflow.
Consider a life reef venturi skimmer, low maintenance no need worry about needle wheel impeller spares, effective skimming and can last you for years after years. I am using one now.