I also think you should possibly consider supporting the passing of nothing / null in the height parameter as specifying the standard height for a gadget for the OS (I assume one exists, at least as a style guidline).
This is an interesting idea... Perhaps, not a null value as that would be effectively '0' for integers (and some people may be wanting to create gadgets with no physical dimensions), but maybe specifying a negative height should set a standard height... Hmmmmm....
Failing that, what would be useful would be some guidelines as to what sizes are appropriate for each OS, e.g. how many chars to allow per character, how what spacing to allow for height, between gadgets, etc. I don't believe it's feasible to cater to all this within maxgui itself.
I know it's not exactly comprehensive, but Skid/Mark did write a little something on choosing the best sizes for gadgets in the "MaxGUI Overview" document under "Tutorials" in the IDE NavBar.