I had no idea you lived in Sweden and Im not sure if newegg ships to Sweden, also you most likely wont break anything because there are instructions for each part, and you dont have to do it in a garage. You can do it anywhere you have enough room.
I think the best choice for you right now is either HP or dell, I prefer HP for their laptops and desktops and they are rather cheaper, they have High Performance computers with a 6 core processor starting at $599. They also have ones around $450 with dual core i3s, check them out.