6/10/20 update:
Starting off with an FTS because I love 'sunrise' in the tank.
I've been testing daily for the past week and a half, and have confirmed that my tank is consuming ~0.5 dkh/day while calcium has remained stable (after an initial, weird result that was likely due to inaccurate testing on my part while getting used to the API kit/comparative inaccuracy of it).
I've opted to dose 0.5 dkh of alkalinity (Red Sea Foundation B) daily to maintain 9 dkh while leaving calcium alone. My rationale is that, since consuming 2.8 dkh of alkalinity consumes only 20 ppm of calcium, calcium will be maintained with weekly water changes (and dosing alk daily will help prevent larger swings when I do water changes). I've been monitoring pH/salinity/etc like a hawk to ensure this doesn't have any untoward effects.
Additionally, my wife and I decided to spend our day off cleaning the apartment. As a reward, we went and picked out a cute ocellaris clownfish. Meet Bartholomew:
I know this is not news to anyone but me, but man - clownfish are weird. He spent the first two days swimming so hard that I was concerned he was going to drop dead from exhaustion. He's finally calmed down a bit and is mostly hanging out in the front right and back left corner of the tank, but hasn't given the anemone (or anything else) a second glance.
Sadly, we're back to having only two fish in the tank. The clownfish has been remarkably peaceful, but it's made the bar goby spend a lot more time out of its burrow. This led to (I'm assuming) redirected aggression towards the firefish. A couple days ago I came home to the firefish flopping weakly on top of the tank lid (it had jumped through a crack less than 1/4" wide and somehow landed on top of the mesh). I added it back to the tank, but it didn't do well (and wasn't helped by the bar goby grabbing it by its gills and dragging it away from the burrow). Poor thing passed away shortly afterwards...and my first indication was that the cleaner shrimp was eating it.
I retrieved the body from the cleaner shrimp after chasing it around the tank for five half-infuriating, half hilarious minutes. Footage of the shrimp during this chase provided below: