I am concerned that an add-in of my design is ballooning to become
unwieldy. Does anyone have any tips, advice, warnings about splitting
it up over several add-ins, only a few of which are loaded at a time to
respond to user actions?

Or would it be better to leave in a single add-in? What is the size at
which an add-in becomes too large?

I know these are all vague questions, but even fuzzy answers would be
better than none. Thanks!