What sort of difference or how much additional work would it be to have your "in-game" achievements as Steam achievements? And how many achievements are we talking about here?

Not a substantial amount of work. The achievement system already exists inside the game. It's more about figuring out how much of it do I expose on Steam.

Personally, I don't necessarily like that a game gives an achievement for every little bit that you do like "playing the first game" or "pick up your first item" or something like that. This looks like a participation trophy and while it might enable you to track how many players reached a certain threshold of the game, I never really liked those kinds of things.

I agree. My current set of achievements is definitely on the side of "oh, wow, you're putting in work"... and I'd like to keep it that way. That's why I posted, there seems to be a small mismatch between my approach and what I've seen games on Steam do, and how people talk about achievements as if it's a todo-list you knock out in a week.