You will want to avoid Inverness like the plague. Stalag 47
Kirkwall is a great visit, as is Shetland, but to take it all in it would be more than 10 days I think. I found Kirkwall staff, given it is HIAL, really friendly and helpful, which are words that generally do not appear in the HIAL customer service plan.
MJ from memory, I thought the bus service into town was ok
He is going in a Cub, so fuel planning, unless it is Mogas, is a thought. But that would form part of any flight plan
Bags of options, and Mono let us know what you plan.