Alright, so it seems that the server ticks are determined how you program RPCs. If you put them in _physics_process, it will tick 60 times per second or a custom value.
So to control the tick speed, I just plug in my network sync functions into a process node.
I’ll figure out my last 2 questions, then edit them here.
Edit:
For question 3: It is very unlikely that server updates (ticks) need to by synchronized by an external system.
For question 4: The ideal tick rate for multiplayer PvP shooters is between 60hz and 120hz. 120hz is unnecessary and costs too much. I choose 60hz, as that’s the default _physics_process update rate.