/bg numactionbars <value>, where <value> is how many actionbars you want.

There's a hard coded limit of 120 action buttons, it is not possible to go beyond that unless Blizzard decides to up the action button limit at some point in the future. However, if you want 12 bars of 10 buttons each, or 120 action bars, each with one button each, its now possible with Bongos.

Currently, there isn't a way to configure actionbars past 10 using the main options window. You'll have to use slash commands and the bar's right click menu.