Level 25 (and since it's practically the same, but harder, Level 50, too) is now in the game.
At first I was GROSSLY overthinking the concept, but after a bit of simplification, it actually turned out really rather well.

I've had to stress test both levels to ensure they're completable, and am happy that they are at least do-able by myself. .. Meaning it probably won't be too hard for other folk!

Anyway, they're done.
Now I just have to make levels 26->49, and we're ready to go!!!