We are just back from there and had a great time.
Overnight ferry from aberdeen unless you are a real light sleeper then I wouldnt bother with the expense of a cabin sleeping bag and kip on the lounge seats you wont be alone, least you get to lie flat the aircraft seats only recline gave up on them years ago.
We were in Shetland for The Simmer Dim Rally but had a few days before to tour around, went to Unst the most northerly island, if camping you can camp at the hostel in Uyeasound costs £6 and you get to use the hostel facilities.
Folks are real friendly, petrol is not so friendly cost up to £1.56 per l so I was a cautious fuel conserving rider sometimes. If you dont intend camping I have a contact for self catering in Shetland bikers own the property just email for info.
Orkney 2 years ago we went for 3 nights stayed 2 weeks, the main camp site in Kirkwall is fantastic has everything you could need and more. There is a free wild camp site on Hoy at Rackwick it has an enclosed garden with a bothy which has a toilet & running water.
A visit to The Orkney Wine Shop on Lamb Holm next door to The Italian Chapel is a must try the Orkney Black Portent the Sloe & Bramble stuff is real good as well.
Roads on both islands are fantastic a lot less potholes than we have on the mainland.
I am thinking Western Isles later this year so you could send me some handy tips if you have any.
Enjoy the trip
Only dead fish go with the flow