I think what is more important is to organize multiple control projects.
I have a control that is used in every other control, so I call it Common. That way I can go back to the core of the controls and make one change, that updates throughout all the other controls that depend on it.
I like using multiple controls, that way I can sell core controls to customers that have the basic functionaility, and controls that prepare my unique data to feed to the core controls, that process it, and return unified values.
Just remeber to clean and build when working with multiple controls.
FYI,
I pack many controls into a single control project. Some projects have up to 30 or 40 controls inside it. But there stored in individual files inside. I also embed all the artwork as well, everything that is needed to produce the control.
I lost control of all the artwork like icons and buttons years ago, so now there all embedded.