I was planning on doing a multi-monitor setup however I would like one of these monitors to be a projector for home entertainment, so I would not want it as my main display. My idea was to use it as a 4th display. Would this be possible with DisplayFusion software and given the proper video card outputs?

Yes, I can confirm, windows really doesn't distinguish between a projector, monitor, or tv.. (I have used all 3, at the same time with my system before) They should all work flawlessly without any special installations...

And yes display-fusion is unnecessary for that specific feature.

Personally, when I had my projector, I had it setup to CLONE my main display (because it was set up in the other room) and would just throw a hotkey that toggle my secondary screen before I left either room.