Just because you can doesn't mean you should though.
Have a read of this article: http://www.tomshardware.com/reviews/radeon-r9-295x2-crossfire-performance,3808.html
It's a pretty messy affair trying to get 4 GPUs to work effectively together. It sounds like they make gaming worse almost as often as they make it better. Your money of course, do what you want with it, but just do it understanding what you're getting yourself in to. Good luck.
It can be done. But power supply requirement will be on very hefty. For games scaling will be issue and knowing some games does not even support multi GPU at all the money spent on such setup are not worth it.