If the support is a simple un-guided pipe shoe, you have only +y.

You would apply friction at this restraint (typ 0.3 for metal/metal or maybe 0.1 for teflon or whatever your situation may be).

Stiffness is an iterative process. You'd likely start w/ the default Caesar assumption that it's rigid, calculate the force, pass that to structural and go back and forth until the structural is happy with the load and displacement. Like you said, with only friction the horizontal displacement is going to be very low unless there's wind/seismic.