If you're based in Ullapool, then I'd have thought you would be looking for a boat that will give a dry-ride, and is able to cope with the rough stuff. Kind of par for the course considering a short distance out of Loch Broom and you're into the Minch!
I'm in Ullapool heading to Lewis around the last two weeks of July, date to be confirmed. I'll be hauling a RIBcraft 4.8m commercial if you want to check it out.
Quick summary (based on my experience of boat and engine dealers in this part of the world)!
(Aberdeen) are effectively a commercial sales and service agent. They are an approved Avon repairer, and also deal in Zodiac Mil/Pro. Also main Yamaha sales agent. Limited supply of used engines in stock. Graham the owner is very knowledgable, but don't be surprised if he doesn't return emails... his work is almost entirely oil-support fast rescue craft and he's always out the door with work.
(Inverness) are Avon and Yamaha dealer. Has repair facility/workshop and decent chandlery. Again, difficult to get emails and queries answered. They seem to be more geared for hard-boats, yachts, etc.
Gael Force Marine
(Inverness) are a well-stocked chandlery, outboard repair and sales agent. Seem to specialise in Suzuki and Honda outboards. They can also source Tohatsu spares. Also have mail-order service which is great for things like impellers, stainless steel bolts, etc. Can recommend.
Sea and Shore
(Dundee). Mariner engine and Raider boat sales. Euan, the owner is knowledgable and does the marine servicing side. Has some engines for resale. Used to be a Zodiac dealer - but I don't think that's the case any more.
(Edinburgh) has just merged with FYM (Grangemouth). They're an Avon, Zodiac and RibX dealer, and supply all the main engine brands. Limited selection of used engines and RIBs for sale. Expensive in my opinion.
(Glasgow) are a Premier Zodiac and Yamaha dealer. Very knowledgable, but priced for top-end of the market. For example Zodiac Pro 550 and Yamaha 70hp for £21k.
Clyde Outboard Services
(Gourock) is a small business run by Cameron. He can source new and second-hand Honda and Tohatsu engines. Again, very knowledgable and always returns emails and phone calls. Can recommend.