According to the
specification sheet, the ASUS ROG Strix B350-F Gaming has 3 fan connectors for chassis fans, + 2 fan connectors for your CPU.
So in total, 5 systems fans (3 chassis, 2 CPU).
Of course, you can always
buy a fan hub to have more fan connectors if you wish to use more fans.
Hope this helped!
-Lachlan