Thanks @LatteYou have a BEAUTIFUL tank set up for Oatmeal and definitely room for a couple fish to swim around at the top. I hope you persevere!
Two quick notes: I will lean HEAVILY to the safer side of glass boxes full of salt water in your house... But there's no way that mantis breaks your tank, let go of that anxiety .
Also, corals are really more like plants, I would never cycle a tank with inverts or fish in it, but cycling a tank with corals or algae in is often actually a good idea in my opinion and is likely to lead to a greater chance of successful/diverse biome in the future. I obviously wouldn't actively try and kill a coral, but they are ethically (in my personal opinion) better viewed as plants than as animals in terms of their capacity to experience any feelings of emotions, pain, stress etc. I think corals being animals is more of a quirk of the scientific definition, than a representation of their capacity to feel or suffer.
Yeah I agree with you on the ethics of cycling with corals but as @Tired said it may be a questionable strategy just in terms of having the corals thrive. I'm not in a rush to get to that point anyway. My nitrites are stubbornly high at the moment (still around 1.5 this morning) and it'll be easier to eliminate that problem if I don't change anything else in the meantime. I want to get nitrites and nitrates down to safe levels before I start introducing anything else, not least because I suspect I could make those existing levels go even worse if I start experimenting with corals or fish, and that could put Oatmeal in greater harm than she's already in, poor thing.