Thanks, all of you for great suggestions. I haven't tried them all out yet, but I will as soon as I get a break from my "real" work.
In the meantime, I think at the root of a lot of my problems is that I haven't found detailed documentation for the App Builder (AB). It must exist, but I can't find it. Does anyone have a link?
For example, I didn't know what the "Script" field in the Properties menu of AB was for, and I didn't make the connection with the Number Edit Box (NEB) documentation. I'm groping my way along here, obviously.
Another example of my confusion, the "Increment" entry field in the AB Properties pane for NEBs exists, but won't accept an entry. I could go on…
Like I say, some good documentation on AB, and also some excellent examples of complex modal dialog box scripts would be great. Also, is there a way to actually see the code that AB generates for the interface?