I also don't understand the use of the HOB. You should be able to get all the water movement you need in the fuge with the return pump, the HOB is redundant. <If you want to keep a filter seeded, just pull the pad & put it in with your scrubbie things.>
I also agree with Capt'n. No need to go 3 chambers. Remove the baffle where the HOB sits, and you can have the entire area as a fuge.
For the return pump, you might want to invest in an auto-shut off model. <Or have an auto shutoff switch.> A 10 is small enough that evaporation can drop your level in your pump chamber enough to fry the pump. Alternatively, you can dispense with the bubble trap & have a single compartment sump ... prob a better design for a small sump.
For reference - my 30 gal sump is single compartment (except for the biomedia basket on top like you have), and I need to top up weekly before the water level gets too low for the pump. <That is an enforced weekly pwc for me ...>