3-way or 4-way SLI will require a 4-way SLI-certified LGA 2011 motherboard. You can do 4-way with a GTX 980. Just make sure you have a quality 1000w+ PSU and at least an i7-5930K CPU. Even a 4820k will not cut it in this situation.
It is, but there are better things to do. Even for 3x 1440p monitors you could just go for dual 980 sli. 3x 4k screens is impossible with current GPUs. You would want a 4790k, 8-16GB RAM, and other things. It needs a bit more planning and detail first.
you're going to want a cpu with 40 lanes of PCIe first off. so an i7 5930k or higher. or older gen i7 4820k or higher. anything lower than those 2 cpus only have 16 PCIe lanes. then youre going to want to get yourself a $250+ motherboard. you CAN do 4 way sli on a z97 platform via a motherboard with plx chip, but i really wouldnt recommend it.
3-way or 4-way SLI will require a 4-way SLI-certified LGA 2011 motherboard. You can do 4-way with a GTX 980. Just make sure you have a quality 1000w+ PSU and at least an i7-5930K CPU. Even a 4820k will not cut it in this situation.