If you do not use child themes for each theme that might

If you do not use child themes for each theme that might be used, any changes made to the theme will be seen and used by all on the network, correct?

So, I've been told that you need to create and install child themes.

I know I will be using at least these themes: Blog MU, Classifieds, and Business Directory. So, how do I make child themes for each one I want to use?

Now, if I do use child themes, then each users changes will only be on their site?

Then they need to select the specific "child" theme to activate on each individual site on the network, correct?

Anything else to know?

Tom