Very nice - both the core mechanics and the exploration of the mechanics with wildly varying ideas. There's no filler here.
I'm not normally a fan of physics puzzles (too imprecise) but I was happy to play these out. I really appreciate that you were very open about being able to skip levels. I did skip some that were a bit too hard but I feel like I got the value out of them anyway, and because of that feature I was able to see it through to the end. Nice job!