Trying to test on a fresh install of Debian 9.4 but setting up homekit-controller failed due to missing dependencies - have you added a section to the docs somewhere that notes the required system libs to install gmpy2 (a dep of homekit)? Looks like gmp, mpfr, and mpc.
Edit - to my base Debian install, I needed to do:
apt install libgmp-dev libmpfr-dev libmpc-dev
Before pip install gmpy2 would work inside my HA venv.