Frank, given your expressed preferences, medical questions, and limited building experience, I was going to suggest some of the more ultralight-style (Dacron fabric over aluminum tubes) kits, but then I saw that you wanted to keep the initial investment small and pay as you go. In addition to the options you've mentioned you might consider the Corben (not Pober) Junior Ace, a little lighter than Paul P.'s redesign, plans are still available including a trigear option. There is also historical precedent for fully enclosed Corbens as you can see from the second pic below.
http://www.aceaircraft.com/
You might also take a look at Leonard Milholland's designs, especially the Cabin Eagle. They are simple planes, well proven, and the Cabin Eagle is simple the latest evolution. With a few fairing strips, a J-3-style cowling, and the right color scheme it could look very classy as well. It's also designed for VW power which can be another way to save money.
http://www.betterhalfvw.com/cabineagle.htm His planes and plans are much better than his awful web site ;-)
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