I've been doing something similar with some friends of mine for fun instead of work, but the concepts are the same. I purchased a relatively cheap Wacom knockof

I've been doing something similar with some friends of mine for fun instead of work, but the concepts are the same. I purchased a relatively cheap Wacom knockoff from Amazon and have had very good luck with everything about it, from the pressure-sensitivity to the Linux support. Depending on the software, the pressure-sensitivity might not work so well, but that shouldn't be an issue for whiteboard-style usage. My recommendation is that you use a 60% or tenkeyless keyboard so that you can comfortably fit the drawing tablet to the far side of your mouse on the desk and still be able to type. Having a trackball is nice since it means that you don't have to give yourself a large area in which to use the mouse. If you're ambidextrous with the mouse, this won't be an issue.