Thank you! Lots of food for thought here. I've taken a crack at Godot so far, and run through some tutorials. I'm still clunking along a little trying to pick up all the terminology and quirks, but getting there.
My aim so far is to keep running through tutorials until I have the skills to be able to create a small aspect of a running sim; perhaps "goodies" "baddies" and "neutrals" nodes that will interact in a simple 2d scene, then practice layering complexity up from there until I'm fluent enough to shoot for what I want.
I'm setting an expectation for myself to have something working in the next year that looks vaguely like it's a part of my initial idea (or whatever that idea has evolved in to like by then).
Programming-wise, I'm still groping around in the dark for the most part, but from what I've seen I think this will start to make sense to me eventually. This whole idea started while I was watching the third series of Britannia, and not being able to shake the concept, I ended up creating this spreadsheet in Google Sheets that simulates combat interactions to sort of exorcise this brain itch I was getting. (Apparently, it wasn't quite enough.!) I'd never really used Excel before, so it took a bit of research. The jump in complexity and what you can achieve in Godot's native language is obviously huge, and looks like it could provide some great system depth, but even taking that in to account, I've found it a lot more impenetrable just to get that initial familiarity going.
Thanks as well for the engine/framework directory views, I'd not thought to look at the choice from that perspective. And that YouTube is exactly the sort of thing I want to learn to build eventually! Even if just for the graphs :D.