Hello Bart.

(1) Mention the preload by checking the "forces and moments" option for that node and insert you preload as a vector in that direction.

(2)& (3) From what i can understand is that you have a restraint in the Y direction only and the pipe is free to move in the X and Z directions so define a restraint by manually inputting the "Stif" value when you define the Y restraint along with its "Mu". It will use this friction and stifness while moving in the X and Z-axis aswell.

I hope i've answered your query

BR
Umair