- 28 would be just fine
- problem with boom too high is that it lifts your front foot out of the starps (which can be desirable (can))
The main thing is, keep going for it and get a GPS (it really helps verify if you're making progress or not).
Try things out and do yourself a favor: http://www.guycribb.com/windsurfing_...VD_0076v01.htm
just check out ALL the articles the guy has written.
Roger is a great help too, but more "reactive" and less "proactive". So if you run against a wall ask Roger. The link provides tons of insights that will help you progress fasten than mere "trail and error".