The short answer is don’t worry about tipsiness. Greenland style sea kayaks are stable enough that you can learn to be comfortable in them in short order (just low brace into the lumpy water that is bothering you, keep loose at the hips, and let the boat take care of you). Most Greenland derived designs are fundamentally sea worthy and can be a blast to paddle. Why ride a tricycle when you can ride a bicycle? The designs which you have identified are all quite stable.
The long answer is that you should learn more about kayaking before you decide what type of boat to build, and learn more about paddling technique and paddling safety before you head off on your own. You can do these things by taking lessons, joining a club, and attending symposia. Hull shape is hugely important – just as important as picking a proper fitting pair of running shoes. Develop a basic skill set, try out a bunch of hull designs, and then decide which boat to build.
Sea kayak symposia are gatherings of paddlers where issues are discussed, instruction is given, and dealers show their wares. I don’t know about symposia in your area. Just google kayak symposium minnesota and you’ll come up with something. (There is a nice one being held in Rossport on the north shore of Superior on June 21, 22 and 23 which still might have a spot or two open for folks without their own boats. One day of lessons, one day of guided paddling in the archipelago, lots of nice people. Contact Dave Tamblyn at email@example.com) (GLSKC has a big symposium in Grand Marais Michigan (not MN) on July 18, 19, 20, 21. Contact Larry Merx, e-mail: firstname.lastname@example.org)
As far as clubs and lessons go, start your search through the Minnesota Canoe Association (a member of the American Canoe Association), which can introduce you to the paddling community. I can’t overstate the importance of high quality instruction and competent paddling companions. Aside from keeping you alive, quality lessons and competent companions will speed your development and help you avoid equipment and technique problems.
If you want to learn how to handle a tippy boat and are willing to travel to northern Minnesota or Ontario, drop me a line. I can put you in a sprint racing kayak and have you balancing and paddling it within a day (just pick a really hot summer day and expect to swim a lot). Once you learn balancing technique in a sprint boat, that will take care of any stability concerns you will ever have concerning relatively much more stable sea kayaks.
There is a hugely informative (and friendly) group of sea kayakers participating in the Paddlewise mailing list, including professional designers, builders, instructors and guides. I strongly encourage you to drop into www.paddlewise.net and sign up for the mailing list. It is the first and last stop for sea kayaking discussion on the net.
OWWA Wild Water Instructor
OSCRA/NCCP Sprint Racing Instructor
Past director: Wilderness Canoe Association, Canoe Ontario, Ontario Recreational Canoe Association