Wow, this is fantastic. A simple idea executed brilliantly with puzzles that build on interesting concepts and don't repeat themselves.
Challenge 3 is quite the conundrum, isn't it? I've finally solved it but I feel I need a lie down now. I didn't notice any unnecessary crates in my solution, but there is a door whose function I'm unsure of (in the lower right).
On a purely cosmetic note, I feel like the pushable tiles could be a bit more distinct from the static ones. Maybe it's just my eyes, but the grey/black border differentiation could be a little clearer.
Anyway, awesome work and many congratulations on the grant. This deserves a lot of success.