I just want to thank the Pi-Hole team for the project, I run it at home and work and it's absolutely fantastic. Funnily enough, when you get to this many clients/queries, the web interface breaks unless you comment out some html and disable logging.
At home, I use docker. I don't need anything fancy there.
For work, we are better suited for virtual machines, so I run pihole in a "bare metal" install, with nginx to serve the web UI with SSL. It's load balanced with dnsdist, as without it clients would hit only one server and overload it. We also have a DNSSEC implementation on the recursive/authoritative servers that the Pi-Holes handle just fine.
Overall with a couple of tweaks, Pi-Hole is enterprise material in my opinion.