1) The new one will of course perform better.
2) Yes it is probably time if you can afford.
3) Yes broadwell will be better, by how much who knows. Personally haswell-e is a disgrace, the quad-core haswell refresh almost matches in every category.
4) I would wait for the gtx to be released it is only right around the corner
5) Single card in most cases is better because their are still issues being resolved with SLI.