There is no reason why you cannot build an equal quality boat from the plans. We use the same parts file for the full size plan sheets that come with the plans as the cut file for the kit. You do not have to do any scaling or lofting. If you are meticulous in marking and cutting, and use a good quality marine ply, you will have the same boat. You do have to do your own scarfing but you can do butt tape joints, which are just as strong but take extra fairing.
The point that some have made about the huge time saving of the kit cannot be over emphasized. It all depends on your burnout index. If you have a bunch of unfinished projects in your life, starting from plans might not be a good idea.
We have shipped quite a few kits to Canada but we usually get burned because the Customs finds an extra fee or two that was not in the shipping quote. The cost does go up as it crosses the border. We have shipped to an address on this side of the border and the customer has driven over and picked it up. If it can be picked up from a depot, everyone can save a bundle because they charge a lot for home delivery and the mk3 kit is so heavy that you need a truck with a forklift. The lid is just screwed down but drivers cannot wait for you to remove the lid and decant the contents.
As for headroom, at 6'5" you would be much happier with the 20. I was on Carlita yesterday and thinking of you at 6' 5". At 5' 7" my head just touched the underside of the 1" deep beams sitting sitting tall on 2" cushions which squashed down to about 1/2". The extra 2" in the 3.2 version would not be enough for you, not to mention the extra legroom that you will need. After my trip to Port Townsend we brought out the updated MK3.2 version incorporating everything that we had learned. The main modification was to add 2" more headroom in both models. Everyone I talked to at the Wooden boat festival talked about headroom. Most of the the other modifications were to make it easier to build. There is not a lot more work in the 20 as they both have the same building steps. The 20 does have more surface area to glass, sand and paint.