Should I give each developer their own Definition Set / Project Folder?

For training and experimentation purposes you might give each developer their own private definition set / project folder. When doing a real project you should never do this. Projects should be set up on a discrete project basis. Work done in a definition set / project folder cannot be merged with work done in another definition set / project folder. It is normal for multiple developers to be working on the same project with the same definition set.

Can a screen's customization be completely removed?

Yes. Locate the file named Screen_xxxxxxxxxx.js in your definition set folder and delete it.

Before doing this end all aXes developer sessions.

Can a screen's customization be completely removed?

Yes. Locate the file named Screen_xxxxxxxxxx.js in your definition set folder and delete it.

Before doing this end all aXes developer sessions.

If I rename a screen, does AXES automatically remove the old screen file?

No, AXES will leave the old file intact. You will have to remove it manually.