Some of the islands need there own holiday and couldn’t really be done on one ‘package’
Eg
Arran
Mull
Skye
Orkney
Shetland
The outer Hebrides
If you want to do a few islands maybe have a base in Oban and get the various ferries from there?
Use the calmac timetable as your guide. You NEED to book in advance or you won’t get on the ferry on a lot of routes! And you need to arrive at least half an hour before departure!
There is also very limited accommodation on a lot of islands- don’t expect to find a b &b with vacancies.
Think about a campervan/ motor home but the roads aren’t designed fur them (lots of passing places esp Skye) and the locals don’t like them, so there’s not many facilities.
The best circular routes to try are:
Ardrossan- Campbeltown- day trip to Gigha- could hop over to Islay/Jura then back via Lochranza on arran to Brodick and back to Ardrossan then day to Bute up the coast.
Up the glenfinnan viaduct to mallaig ferry to skye, drive up Skye (it’s a big island and this takes a while) then ferry from Uig to Harris then drive up to Stornaway then ferry back to Ullapool.
Be aware of Sabbatism in the outer Hebrides (Sunday closures).