Hi, very nice work, I was suggested this link on the reprap forums after trying to come up with about the same idea for a corexy printer (decompressing instead of pressing onto, no visible movement for triggering).
Are you still developing this solution? What is the repeatability of the FSR solution? I find it one of the best solutions out there apart from a strain gauge that would be way more sensitive but again needs special board/etc. I've read that the repeatability of the FSR is arund 0.02mm (from the Kossel FSR Wiki) and also that the output of the FSR can go straight to the Z_MIN on the controller board.
I see below comments about another board to interface the FSR to the arduino. I believe that is not needed.
Again congrats and keep us updated.