would this product work without having to purchase the pan tilt and 3 axis gimbal?

Yes, the Proaim 18ft Jib can also work perfectly without the Pan Tilt Head and 3-axis Head. You can accommodate small DSLR/DSLM cameras directly on the camera mount top plate of the Proaim18ft Jib.

Can the motors run on 18V DC or should I step down out batteries to 12V?

You can use max battery power of 12V.

What is the wiring information for the 4 Pin XLR connector

The 4-pin XLR connector is used, in which the 4th number pin is used for DC positive, the 1st number for DC negative, and the 2nd & 3rd numbers remain unused

Is this DMX controllable?

No, there is no connection of DMX with the Proaim Jr. pan tilt head.

What are the dimensions of PT-JR

"Here are the dimensions Proaim Jr. Pan Tilt Head PT-JR: https://prnt.sc/fM_LFwh0wXvt "