Gas tank skid would be my first skid recommendation if your's doesn't have it. (After rock rails) That is my next purchase but I haven't hit it (hard) yet.. but it's been close a couple of times.

I think I'd do gas/t-case and leave the trans/motor skids for last. Once rock rails are on, it pushes that stuff even further up out of the way since you will most likely hit the rails first.

While it's at the shop, I assume they have an rti ramp or something to check the flex. I'd make sure its bump stopped right so you don't tear up the tires your first time wheeling it.