I am looking to control zoom; do I need the force joystick?

You can map the zoom motor to any axis on the Controller. You do this via the Controller menu;

MENU - INPUTS - AXIS - ZOOM

By default the Zoom will be assigned to dial 'A' on a standard 4 axis Controller.

The 6 axis Controller includes a Forcezoom joystick. This is the same force sensor as on the Preston Microforce and Arri hand Controller. It is considered the industry standard for feature, drama and commercial work. 

The Forcezoom joystick will provide much more sensitive and precise zoom control. You can upgrade to this at a later date. 

Please note that you also have the option of selecting Zoomspeed as well as the ZAP function.