If yes, how does one determine that maximum? That is the most important part to me. I'd really like to have it be set manually. I considered using runtime.GOMAXPROCS(0), as i doubt that more parallelism will yield any additional benefits. The comment seems to suggest, that it is marked for deprecation at some point.
From what I gather, the only limiting factor when it comes to go routines is memory, as a sleeping go routine still requires memory for its stack.
It's not strictly necessary. The number of threads running these goroutines is by default equal to the number of CPU cores on the machine (configurable through GOMAXPROCS), so there will be no contention at the thread level.
However, you might get performance benefits from having fewer goroutines ready to run, because of memory caching effects. For example, on an 8-core machine, if you have 1000 active goroutines that all touch significant amounts of memory, by the time a goroutine gets to run again, the needed memory pages have probably already been evicted from your CPU caches. With fewer goroutines, the odds of a cache hit are better.
As always with performance questions: the only way to be sure is to measure it yourself with a representative workload.