Well, as a general update, Mr. Mango became ill a few days ago and from what I can tell, died from pop eye and a fungal infection.
I'm awaiting an internal filter to put in the DT for a week or so, then move to the QT and work on cycling it so I can add some panda corys and possibly one or two honey gouramis. After Mr. Mango, the tank feels like it's missing something, so I think some honeys will brighten it up.
I actually found out from a redditor in /r/aquariums that Mr. Mango was a "sunset" gourami, a color morph of the thick-lipped gourami. I was under the impression that honey gouramis have many names (at least looking at gouramis in pet stores, a lot of names are thrown around for a single species), but seeing as Mr. Mango was 3.5 or so inches, he definitely wasn't a honey! They're a little smaller, getting about 2.5 inches. I'm always learning new things in this hobby
I also can't seem to find my little assassin snail, wherever it is, and some pest snails have been popping up, so I think I'll get another assassin and maybe some more amano shrimp as well since they're so fun to watch!