Just happened across this thread when I was browsing for something else, and WOW, am I impressed!!! I've never been on the 'Hebridean Isles', but I'm a "fairly" regular traveller on the 'Isle of Mull', and you've certainly caught the character of the modern ferries.
I'm looking forward to pictures of 'Columba' when you get around to building her as she was the regular vessel on the Oban - Craignure run for many years and she grew on me after a period when going on family holidays to the Isle of Iona.
My real favourite would have to be 'King George V'; now there's an elegantly classic steamer. If only I had the space, but in 7mm scale....
Donald