Hey, I was 13 when I built mine (Like 6 months ago XD). Watch plenty of tutorials, and read a lot too. Just try to build as much knowledge as you can, and don't be afraid to ask questions :P Also, when it comes to building it, don't rush, take it slow. If it doesn't work straight away, don't panic. Oh, and get the cables neat when you are building it!
Also, I run Windows 8, and love it. There are plenty of programs that add a "start menu" if you are desperate to have it, though you might find you like the modern UI.
Nice spec!