I'll definitely give that a look when it comes to editing; I'm happy with my current setup (I'm using Typora for drafting, since all I want is something that puts text on the screen and has some word processing features, and it has a relatively robust pandoc integration.) As for Affinity, I haven't used the suite enough yet (I'm a neophyte Designer user, now looking to extend into Publisher) to really see the limitations on what it handles. I'll probably fall back to the Word export, since that retains the style information I want.
I wasn't aware that find & replace could do paragraph styles! That would almost be the way I'd want to do this, although I'd rather it were, well, automated. Here's the CommonMark spec, but a brief example would be something like this:
# Demo
This is just a quick document to show off how **Markdown** is written. It's a simple syntax, really.
## Headings
Headings are defined by lines starting with one or more `#` characters, followed by a space; the _level_ of the heading is determined by how many
hashes there are.
## Lists
Lists are just:
* one thing
* followed by another
- and can be nested
- when it makes sense
Gruber originally developed it to be something that could readily convert into HTML, and it's fairly easy to parse. The downside of that is that everyone has their own way of doing it, and not all of them are compatible.