You access the extra bars with addons I believe (or using the extra 2 bottom and 2 side bars from wow's interface options). I'd recommend Trinity Bars.

Another note, copying your wow folder for the purpose of having multiple macro setups wont work since those will be held server side too (like the keys).

I would use a bar addon and dedicate a bar for your macro's/multiboxing setup that you can enable/disable as needed while keeping your normal setup intact (keybindings aren't saved server side so you can split up your folders for that purpose).

When it comes to combining buttons you'll want to think about them cos you might not want your shaman to heal every single time your warrior slams and so forth.