Some tips to get you started:
1. Where it's built:
https://github.com/firezone/firezone/blob/master/.github/wor...
2. You'll likely need the following debian packages installed:
dpkg-dev ntp zlib1g-dev libssl-dev openssl bzip2 procps rsync ca-certificates build-essential git gnupg curl unzip locales net-tools systemd
4. I use asdf to manage language runtimes: https://asdf-vm.com