You are on the right track with your research and we highly recommend Four Winns....Melvin Village if you are boating on Winnipesaukee since they will be the main service provider to you. We will go to Melvin Village next season (actually will look for them at the winter boat show in Boston) - since we do our boating primarily on the Big Lake!
We are going with 20 because we of course now have tons of friends who LOVE boating and the 20 footer will afford us a tad more space for all the "toys" we "have to" bring out on the boat.
Good luck with your boat pruchase and happy boating!!