Wow, didn't realize how long it's been since I built this. Guess I'll submit an update.
Still have yet to change the water, aside from top-ups. Now that I have added a proper top to both the sump and tank, I'll have to do a monthly test, maybe. Fish are still super-healthy/happy.
We are now up to...30 fish? ~8 Cardinals, 1 Angel (other two got sucked into the sump), ~12 silver tetras, ~10 Sunburst Platies. All of the shrimp were eaten, unfortunately. I did a water test the other day just for kicks, levels are zero.
The water wisteria died off after I reduced the light window (to combat algae), but the rest of the plants are doing great. The red thing mysteriously came back to life, but still not doing that great.
Anyways...pretty happy with things, and no water changes is pretty awesome. Only maintenance I do is scrub the glass once a month, feed the fish every 2-3 days, and clean the sump mechanical filter maybe once a month. So... 1-2 hours maintenance per month, plus feeding.
Oh...after I added the sump/tank tops, refill period has shrunk dramatically...I'm guessing that will be down to 2 gallons a month, maybe less.