Try using a Mag Float to clean the glass. I use the one meant for acrylic on my BioCube. Occasionally I have to get in there with a clean sponge (one that has been rinsed in both RO and saltwater for days and only gets used in the tank) to get the corners and curves on the glass really clean.
Definitely get rid of the Maroon, it will get too big and too aggressive for that size tank. Maroons are one of, if not the most aggressive species of clowns.
It's probably just a regular bristleworm. I'd say leave it. There the best member of your clean up crew. I only get rid of the larger ones (more than 5").
Cyano is NOT a good thing. It happens in almost everyones tank somewhere though, so don't panic. A small patch is not harmful if it's kept under control. It's caused by lack of flow, too much nutrients (over feeding/inadequate cleaning crew), or bad lighting. Just keep an eye on it. Siphon out what you can with a turkey baster. Look up cyano bacteria which is also called Red Slime Algae for more info.
Flame angels are considered one of the safer dwarf angels to consider. That being said, I personally don't think it would be a wise choice for a Bio Cube. They get larger than some of the other dwarfs and with it being confined in a small area it's more likely to get frustrated with can cause aggression to both other fish and your corals. You'd be better suited with a Cherub, Coral Beauty or an African Flameback if you want a dwarf angel.
It been a while since i was last on here. I was wondering if you guys can give me a feedback on my fish tank! Thanks everyone! 