A sofa-sized throw quilt might be as good first quilting project - not quite as cumbersome or overwhelming as a King size (although, kudos for wanting to tackle King-sized!)
Your room colors might help with the color choices.
Are you traditional? modern? combination? That might help decide upon a quilt pattern.
If you are interested, I am in the process of uploading a Tutorial for a Modern Monochromatic Quilt at
http://destashification.com/2012/06/05/the-mmq-modern-monochromatic-quilt-block-1-and-border/ which uses traditional blocks in a modern quilt. (It is for my modern son - but I am a traditional kind of gal!)
The blocks are paper-pieced so successful and precise piecing is accomplished effortlessly by simply sewing on the line.
Sounds like you have picked up sewing skills quite quickly, so once you work through the process with a smaller quilt, the King size will be a breeze for you!
Good Luck! and keep us posted!