Good questions, but, questions that are FULLY dependent on what your actual budget will be for everything that you need as well as whether you are ONLY going to be changing the CPU, motherboard, memory and graphics card?
Also, it very much matters WHEN you will be doing the upgrade, and I don't recommend even LOOKING at the prices or options until you are within about a week of being able to pull the trigger because market pricing, sales, diminishing availability of last gen hardware, and a variety of other factors can have a tremendous effect on the cost of a given build or whether it is even still possible to do with the hardware outlined if it becomes unavailable, in as little as a day or week, but certainly if we are talking several weeks or months out. In other words, here today, gone tomorrow, has never been more true than it is when talking about the prices and availability of computer hardware. Best to wait until you have the funds and are fully ready to pull the trigger.