Based on your HN username, you're probably not the guy who did the presentation at BSDCan 2015 on the topic of "FreeBSD Operations at Limelight Networks, An Overview of Operating at Internet Scale". Regardless, that was a good and influential presentation, worth the time to google and watch.
I think that specific presentation would answer a lot of OPs questions, probably faster and more accurately than a web discussion board. I got a lot of good ideas from that presentation about freebsd deployment at my workplace. Specifically I seem to recall something along the lines of, its 2016 so start using zabbix instead of nagios, which was pretty good advice, or at least its been interesting to experiment with so far.
I'd extend the remarks from the presentation that much as its possible to write Perl in any language, its possible to do everything linux-style but with a freebsd kernel, whereas the real benefits grow when things start smelling more freebsd-ish and less linux-ish. For example the *bsds are much closer to the proven successful unix philosophy of architecture and design, whereas the linuxes in general have been slowly generally moving away from that successful architecture.
I'd throw out a semi-dissenting opinion that freebsd use is much like whiteboard algo interview questions... even if it has nothing to do with the job or problem, the folks who can do it, are of a class above the folks who can't, so naturally the average freebsd admin being considerably more inherently skilled than the average linux admin results in freebsd deployments requiring 1/10th the number of sysadmin-hours etc etc. There are actual technical improvements and architectural benefits to freebsd, but the main contributor of the often reported 10x benefit to freebsd is the skill, experience, and raw horsepower of the generally superior users. If freebsd were as popular as linux, that would disappear and freebsd users would only be maybe 2x as productive as linux instead of the existing 10x figures. Naturally the guy writing a playbook for ansible will be much more productive than the guy trying to use the gnome GUI to do sysadmin-ish stuff, but there's nothing inherently bsd-ish or linux-ish about it.
(edited to add, yes, i336_, that is exactly the video I recommend)