I would go for the boat referenced earlier, as it can be towed without a hitch.
"Excellent trailer, made 600-mile trip last summer without a hitch, tow her anywhere without worry."
How much boat you need for your family all depends on your family. Some families live in an igloo, some find only 1 bathroom per person inconvenient.
My wife and I just spent a month on our Seaward 25 with two Australian Shepherds.
If I had the truck for the job, I would probably do what you are planning, with a Cat 27 or similar, and plan on a full day to launch and retrieve. Would probaly do it in less.
One thing to consider with the trailer is to make the back bunks or supports adjustable. The middle of the boat is wider than the stern, and will have to pass between the back supports. If they are not adjustable, you will have to go deep enough to float over them.
Post pics when you are done with the project.