Caddy won’t be your bottleneck unless you get to very high amounts of requests per second. Don’t worry about premature optimization.
Sorry, I’m not aware of any that use Caddy v2 yet, @matt might know of some though. I figure this is an area where we’ll need some documentation though.
Alternatively, you could use CertMagic as a library if the main thing you need is automatic HTTPS. It’s the library that’s at the core of Caddy to provide this. There’s plenty of people using it (but unfortunately I can’t really offer any examples, I’m not following who uses it very closely).
I’d go so far as to say ludicrous amounts. Just to back this point up a bit, Caddy is a Golang web server, and not only are these kinds of servers deployed by some seriously huge enterprises in service of major traffic, so far even just for Caddy 2 we’ve seen extremely optimistic benchmarks and extremely pessimistic ones, varying wildly based on what it’s being compared to (e.g. vs. highly specialized / optimized code, or vs. out-of-the-box standard nginx) and what hardware it’s run on.
Caddy v2 will serve you with distinction, right up to the point where you need to eke out every single shred of perf you can, and have the skills and tools required to identify bottlenecks in your servers. At that stage, you’ll already know what you need to do.