General rule of thumb with labs is to build them up to just over your max potential at your homeworld (update i.e. add more periodically, e.g. when you get important new components like energy collectors, LRS, etc.)
Then put 1-2 labs in each research station. You can build a 2-lab research station with 1 energy collector, one of each hab module, a reactor, a couple fuel cells, and a few cargo bays with just your starting techs, IIRC.
A 15-lab research station is not a good idea.
I don't recommend arming your homeworld starport at all until you have Velocity Shards (my weapon of choice because Assault Missiles in late game are **** for DPM unless you modded them), PD guns and Shields, because maintenanace is expensive and early game you're paying off all the pirates you know of anyhow)