Steelseries makes a bunch of different ones at pretty much all price points. I've heard good things about Steel Series Siberia V3 which can be picked up on amazon for your budget. Also there is the HyperX Cloud that has had some awesome reviews and is also in your price range.
I personally would just go with a 980 even though SLI has come a long way its still not perfect and if you can get the same performance (or in this case better) from one card that in my opinion is the way to go.
Really depends on your needs for the case but i just built in the Core X9 and loved it. I definitely recommend it if you have the room for a full sized case.
Yes that makes sense. Standing still the lighting effect would make the gpu usage jump. Then will moving and having to render that light over other objects on the map would also feed more information to the GPU and in turn make its usage jump even more.
I don't know that physx is worth the extra cost. Necessary defiantly not. Not many games out there support it, its just more of a bonus for the games that do. Its not something i would consider when choosing a new card.
Yea it might be hard to find a good "Gaming" IPS monitor in that budget. I personally have 3 of the 248QEs listed above and i love my setup. I have removed the bezels from mine and set them in portrait.