Good stuff Eric! Just a couple of points from my own experience of fishing the Scottish lochs:
I would always go for a planing hull when fishing a large water. When coupled with a decent engine this gives you the ability to get out of trouble fast if the need arises. I can think of at least 2 occasions when I made it back to base when the weather turned when guys with displacement boats had to take shelter and spend the night on the loch.
A 13ft boat is the absolute minimum for fishing a water like Loch Lomond or Loch Awe.
I can thoroughly recommend the Pioneer boats as I've had a lot of experience with them as yacht club rescue boats. They are stable, tough, will plane with a smallish engine and can handle rough conditions really well.
A lightweight folding cuddy makes a huge difference to your comfort in bad weather. A folding cuddy is a lot more versatile than a fixed one.