Basic tips on building a gaming computer?

Ok so I'm building this new desktop that would cost around 1500$ and I need your help. Good news is that I'm not totally clueless and I know a few basics to building a computer. I know that I need a compatible mobo with the proccessor (lga socket) and I was thinking to get the core i5-2500k and a compatible motherboard, but will it be better if i took an intel mobo, asus idk theres just so many to pick from but I'm thinking of taking an intel one, its just easier to pick. As for RAM (DDR3 of course) I was thinking of 6GB (3x2gb? cause idk which mobo has enough RAM slots to fit 3 so help out here) cause thats as much as games would need even like 5 years from now. But would it make much of a difference if they have different Mhz for gaming? As for the video card, please suggest some fitting ones that are sensible for this system but no lower than 460gtx please, should I use dual cards or one powerful card idk. Also for the vcard is that will it fit in the motherboard, or does it have a different slot that requires something else since thats what I heard is the case in powerful video cards. I would appreciate any answers that would help me out cause im kinda confused about a few areas.