Another river user here. I like river, but I wouldn't recommend it (for someone who's never used a tiler). It feels a bit bare bones and there's not that much development going on (still active, but not frequent updates).
Both Sway and Hyprland are probably good picks. You can always switch to a different one, if your first choice doesn't satisfy you.
That programming as a career means you're going to spend writing nice, clean code 80% of the time.
It's rather debugging code or tooling problems 50% of the time, talking to other people (whether necessary or not) about 35% of the time and the rest may be spent on actually spending time doing the thing you actually enjoy.
I may be exaggerating, but only a little.