heres some advice don't overclock until you know you are ready to take on the task and also have read all you can read about it. No you don't add both cores. each core runs at 1.86.
Don't look at the GHZ it LIES!! research on this
If your new to computer i would research a bit more before building any. jsut look around at hte reviews. We can tell you what to build but unless u have read about the parts you don't know what you are building. You become moe involved when you research what hardware you want to use or what could be better for you money and stuff like that. There is alot of thing about it then jsut getting hte parts and slaming them into a case.
You should make a part list out and if you have any troubles we well help. We can sit here all day giving you all differnt components but you might not understand why we choice that peice of hardware. You well be better off picking your own parts cuase it well take some research and you well get to know what you are buying much better.