Typically with the TT level and TT & TV loaded for camping, you set the ball 1" higher than the coupler to allow for squat in the TV. But if you don't know the frame height, I would guess low so that the TT nose is down rather than up. If you have the tools at home, (sounds like you do), set the ball height when you pick the TT up. You may need to adjust the bar angle too when hooking up the TT and may need your tools anyway.
If picking up at a dealer, whatever you do don't let them anywhere near it.