What is the MAX pixel estate I can get from a MBAir 2011 with multiple displays?
As has been said in the other answer, you are restricted to a single external display with the built-in hardware.

You can however add extra external displays using USB based display adapters. For example I use one of the DisplayLink adapters. Some of the DisplayLink adapters can do 2048x1152. There will be a limit to how many USB adapters make sense, before you start saturating the USB bus. But it should be fine for a couple of extra displays.

USB based adapters aren't well suited to 3D gaming and full screen video, but should be fine for what you want.