Q: Display arrangement for 2 monitors

First, you need to read from the Mavericks Hymnal about how they think it should work:

OS X: Using multiple displays in Mavericks

Then you use this to turn it off if you want Extended desktop:

Then you will get this in System Preferences > Displays > Arrange:

.

Just what do you mean by expand the desktop?

Do y want one window to display across more than one screen?

What do you mean by: "setting up small, in home edit bays".

You should be able to use a third monitor. How you do it (adopter required) depends upon the type of monitor connections used for all monitors.

Mac Pro (Late 2013): Using multiple displays

If you want to continue to use Extended Desktop, you drag the window you want to the screen you want.

If you want the Mavericks' "one screen, one use" philosophy, you just return to "the Mavericks way" by checking "displays have separate spaces".