Great question — answering as the UphillTech team:
I'm not very familiar with FreeBSD specifically, but the traditional Linux/Unix way is to start things through your login shell's configuration, i.e. ~/.profile for sh/bash/ksh or ~/.login for csh. That is, you just add emacs --daemon & somewhere near the end of your profile, optionally with a check to make sure it's not already running, or to run it only if $DISPLAY is set, etc.
Full answer by grawity: https://superuser.stackexchange.com/a/1729891 (CC BY-SA 4.0).
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