This is a rough first draft of what I've come up with so far - I would appreciate any ideas, corrections, tips and so on. I'm very flexible and could even stay a few days longer if I need to. I have not booked my flight yet, but anticipate flying to Scotland around the last week of April or the first week of May (mid-week). I'm flying Delta since I have credits and will probably fly into and out of Edinburgh.
Day 1: Arrive in Edinburgh (2 nights)
Day 3: Train to Glasgow (1 night)
Day 4: Get rental car. Drive to Ardrossan and take ferry to Arran (3 nights?)
Day 7: Drive/ferry to Tobermory (4 nights)
Day 11: Drive/ferry to Isle of Skye (Portree?) (4 nights)
Day 15: Drive/ferry to Harris (2 nights)
Day 17: Drive to Lewis (Stornoway) (3 nights)
Day 20: Ferry to Ullapool, then drive to Inverness (Culloden) (1 night) ?
Day 21: Drive to Loch Lomond (1 night) ?
Day 22: Drive to Stirling (see Stirling Castle), then on to Edinburgh. Return rental car (1 night)
Day 23: Flight home
I do have some questions. The itinerary above is based on the idea that I will have one rental car and will be driving it onto ferries and so on. Is that the most efficient way? Or is it better to rent cars in segments? From what I could see, the car prices on the ferries did not seem unreasonable.
From day 20 to 23, I was planning on driving from Ullapool down to Edinburgh and spending 2 nights on the road. I picked Inverness/Culloden and then Loch Lomond, but I'm definitely open to other places.
I was really trying to figure out how to get in a few days in the Shetland Islands but I don't see how without giving something else up. Maybe Arran? But logistically it would be take some time to get up there, so probably it's not feasible.
Thanks for any help you can give me!