I have run a 15m (50ft) Cat6 cable from my modem on the main floor to the basement entertainment unit. At that unit I have a PS4, TV and Fire Stick. I want to connect both the TV and the PS4 to ethernet for now (Fire stick later if I buy the adapter). Do I just need a splitter at the entertainment unit end of this cable and will be good to go?
Later, if I get an unmanaged multiple-port switch for my main floor devices, can/should I connect this cable to the switch on the main floor, or should I leave it connected straight to the modem?
You’re planning it incorrectly. Generally ALL jacks need a single run back to the basementUUtilities/Comms area of home where the large main switch is. The internet feed should also enter and terminate there. Then devices are connected or patched to wherever in the home you need.
Wiring 1 room to another is the wrong way to do it.
DON’T use network cable splitters, use at minimum a Gigabit switch with enough ports to do what you need, ideally with extras