Seems like you're doing pretty well so far! I'm a big fan of bumblebee gobies and have been keeping mine for a while. Quick question, though. I saw in an earlier post you had mentioned aquarium salt. Did you buy aquarium salt or a marine mix salt?
Aquarium salt (the kind that's manufactured for freshwater aquariums) doesn't actually give you a brackish tank. You need marine salt to convert to brackish.
Your pH should be in the 8.0 range. And you really only need a protein skimmer with fish in larger setups. It wouldn't hurt! It's just not necessary for bb gobies.
And I keep my bumblebees at 1.008-1.010