Is the other area for a fuge then?
Sound slike you will have to plumb a skimmer in through bulkheads.
You can't use ASM then, because they can slowly leak, so they are in-sump only.
Euroreef will do this, they are more pricey.
With a refugium and 40g total water you could get away without a skimmer, just keep on top of water changes. I think you will find your 30g will fill up so quickly you will be wanting a 180g in no time, and can buy a nice juicy skimmer then.
You could go with a CPR BakPakII, or better yet a AquaC Remora in the meantime, the Remora would sell on the used market no problem once you are ready to upgrade.
Oh and even easier, just hang your skimmer off your 10g sump. You might have to install a baffle to make the first chamber high enough for the skimmer, depends on the model & setup of your sump.
Or maybe you will be happy with 30g......... ah who are we kidding.
You'll have a fish room in no time!