For the purposes of inclusivity I hope all four nations are represented in the coaching team because we've seen before what happens when there are 50/50 calls with nobody to push some players' case at the selection meetings. That said it's his coaching team and he should be allowed to choose people he trusts and in his view are most capable to help deliver a winning series.
If Shaun Edwards doesn't tour then Steve Tandy could be an option as defence coach again. He's Welsh, knows the Scottish players well and between him and Faz Snr you've got all four nations represented already.
The head coach needs to be of the same mindset as the rest of the coaching team. The last tour was ridiculous with Gatland and Townsend having completely different styles of play which led to some very mixed up selection.