What you need is an i5 or better. 650w psu if you want OC a single gpu system, 850w suggested if you plan to OC SLI gpus along withan OCd CPU. 8GB of RAM should be alright but I say 16GB because games are going to use 64bit, watchdogs is supposed to be 64bit only, the other reason is games like Skyrim can use the extra RAM when you change a few settings like uGridsToLoad which tells how many cells should be loaded within distance to player, I can really see TES VI using up a lot of RAM if you try these settings, which make the game much better.
I say go with single fastest GPU on 20nm you can afford at the time. Then as games get more demanding look into SLI. I also suggest the ASUS ROG motherboards because of the quality ASUS brings to the table with them. Seasonic for PSUs. Noctua fo cpu cooling.