More importantly everything you ask is in the comments in the code, and the specialized heavy lifting is all separated out into the only other .m file. I'm left to wonder: did you even look at the code?
on another note, Tabs in guis is over a decade old (VB anyone?), that mathworks can't figure out how to add this to their basic gui builder is beyond ridiculous.
To organize complex guis, I now just have one gui call another because it is a pain to go back through LAYERS of objects to edit any of them.