Running 3 at once is going to be determined by what your video card is, can you post what card you have?
An easy way to find out is to type "dxdiag" into the run area, then click on the "display" tabs, depending on whether the motherboard has an integrated card you may see multiple tabs labelled display and they may have different information on each.
As to your question about running a combo of different ones? absolutely.
You should actually be able to set up "profiles" in either the AMD Control center, or the Nvidia control panel, that allow you to quickly switch between different setups (two on your desk, tv and one on the desk, other one on the desk and tv) regarding which monitors are on, and where they are oriented (left/right/above/below) in relation to each other.
if you dont want to go to that extreme you can easily change it in the windows screen resolution settings.