Hi, losrichins,
Looking at your most recent post, it looks to me as though your life (lives?) would be a whole lot easier if you just hired a car for the entire holiday. That would eliminate having to worry about flight/train/bus schedules, and would allow you to travel wherever and whenever you want (ferry schedules permitting!).
The only part of your holiday which would would involve more travel time would be travelling from Glasgow to Islay. It's a bit of a drive to Kennacraig for the ferry, but generally Scotland is better seen from the road than from the air. This would also mean that you would also have a car that you've gotten used to by the time you get to Islay. It would also make getting over to Port Askaig for the ferry to Jura a lot easier, as well.
If you do decide to include Bute on your itinerary (and I definitely would!), ferries from Port Ellen to Kennacraig, Tarbert to Portavadie, and Colintraive to Rhubodach would put you on Bute by mid afternoon, with enough time to visit Mount Stuart. Don't miss the Kyles of Bute overlook at Tighnabruaich.
On day nine, unless you have your heart set on visiting Loch Lomond from Balmaha, you could cut off a long drive (since you'll still have your car), by taking the ferry (no reservation required) back from Rhubodach to Colintraive, taking the A886 to the top of Loch Fyne, then the A83/A819/A85 to Oban, for your ferry to Craignure and the Isle of Mull. If you really wanted to see Loch Lomond, you could turn right instead of left on the A83, and visit the loch at Tarbet, as isn31c recommended. If you do that, you could then double back on the A83 as above.
On day 15, you could then take the ferry from Tobermory to Kilchoan, as isn31c recommended, then drive to Lochailort for the A830 leading in to Mallaig. From there, it's the ferry to Armadale, and about a 90 minute drive to Portree.
After your time on Skye, as isn31c pointed out, there's not a whole lot to see in Duirinish, except possibly for the Highland cows wandering about the street (drive slowly!). Plockton is one of the gems of the Highlands. Lodging reservations, if you decide to stay there, are really a necessity. A couple of the good B&Bs have closed either due to retirement or new government regulations.
Plockton to Aviemore/Kingussie/Newtonmore is a little over four hours drive. Probably closer to five, as you have to negotiate Inverness. It's very scenic for the most part, except for the A9. Watch your speed there!
Okay, I hope that has given you more food for thought! As I said at the beginning of this screed, you'd be better off having a car for your entire holiday. It will be easier, luggage wise - you can live out of your car boot as opposed to having to carry it from pillar to post. Please be sure to make reservations for the ferries, except for Tarbert to Portavadie and Colintraive to Rhubodach, which are show up and go.
I think that if you take all of the advice which you've been given, especially from Mardee and Stuart (isn31c), you are going to have a wonderful holiday. But the final decision on where you want to go, and what you want to see, is up to you!
Very best wishes,
Mike (Auchterless)