Clear,
I'm wondering if I gave you the strumming advice; that's the kind of thing that I tend to do. And when I do it, the goal is to help people, not have them second guess themselves.
I've been working on some upcoming free resources to get people playing, and I have put much too much thought into things like strumming location.
What we're going for is to strum somewhere that:
1) You are approaching the "sweet spot" of the strings
2) Over part of the fretboard.
As I have taught ukulele to hundreds of students over the past 4 years (middle school and elementary, not privately), once you move that strumming below the fretboard, kids get their fingers stuck in the strings while strumming. I'm not joking. You could make some pretty good "Funniest Home Videos" from what I've seen.
And many of us came from guitar influence where strumming is over a sound hole. People think the ukulele is a little guitar, but the ukulele itself has no direct linage to the guitar--it comes from the melding of two Madieran instruments...one provided the tuning, the other the size and number of strings; and then Hawaii itself provided the lumber and string material that was to be used. So we don't want to be imitating the guitar, either.
As for the question about size of ukulele to height, that's all a bunch of hooey in my opinion. While some people gravitate towards a scale they like to play from a point of comfort and sound, others play everything and choose what to play based upon other conditions--going for a specific tone quality, or a practical issue like having to travel with a ukulele on a plane.