A few updates. Went through a mini-mini cycle, but once that was complete, I added 2 more tetras, 1 oto, and 1 platy (temporarily housed while we work out what's up in my mom's tank; also a gift for her). Got 2 bags of larger stones from the dollar store, just looking for some coarse sand to mix in.
Had to shelf the DIY filter for the time being sadly. However, the one that came with the tank was TERRIBLE, so I definitely had to replace it. Found this one and I'm in love! Tetra Whisper i20...it's truly silent and I don't have to turn it off to change the water. It basically disappears against a dark background and has suction well spread out so it moves a lot of water without sucking everything in its path that doesn't move in. Only problem is that it is big and there's a big white sticker right inside the intake. Overall, though, really great filter.
To show how well it disappears:
The temporary occupant
Whachu lookin' at?!
Also, the joys of having really hard well water. Less than a month and already there are substantial mineral deposits.