I don’t have an answer for you, but I will tell you from my experience, you can probably run a lot more on that thing than you might think.
I run all of my services on docker and I think I have 30+ services up at all times. What you should remember is that even under your most demanding workload, you’re probably only hitting like 5 services at a time while the rest sit idle. And if you are picking good, efficient apps (I really like the linuxserver.io apps), they’re not pulling much under load and certainly not while idling.
Your NUC sounds much more capable than my BeeLink and mine doesn’t break a sweat. The other commenter had it right, just keep adding stuff until you see a degradation of performance, I’m yet to hit one.