you better have some fancy tools my man, bottom bracket, headset, and fork are not exactly something you should do if your not familiar with and dont have the right tools.
You shouldnt worry about a frame being in the 5 to 7 lb weight class because it also depends on the parts you put on. You just better hope you have an extra 700 bucks to get parts, and that being pretty cheap. You should check out pricepoint.com they have build kits.
If you get every part one by one and want to get the best stuff, your gonna go into the thousands of dollars believe me i was ther in your situation, its not a cheap hobby.
Your willing to get a cracked frame but not willing to get a used bike?