I think it works well with the `45ch` limit. I think what you have now in your regular app works better with articles and such, like Medium or Ghost, where texts could be long.
Of course, I'm not the high authority on these matters; if people tell you that the column is too narrow, do take their voices into consideration: that's how you become better as a developer and a designer.
> I also wonder if you have some ideas on places I could potentially advertise to
I'm not much for a marketer. I just make things.
If I made an app that I wanted to present to the world, I'd look for places where there's demand for what I made. If I make an app that's good for writing long texts, I'd show it to writers, journalists, bloggers, script writers... – anyone who could use such a thing. Seems like a reasonable thing to me: you want those to see it who could engage with it meaningfully.
So my guess is: figure out what kind of an audience you want, and what kind of an audience Midnight's best suited for, and show up there with the app in hand.
For scale, you could advertise to Product Hunt and post it as an alternative to other products.