Conversely, you could google the ERD, and find that Sun has it listed on their website.
You take the ERD number, go to king's website and get the hub wheel building specs, and plug all of those into DT's wheelbuilding calculator, which again, you can find via Google. I would highly recommend not using aluminum nipples for a first wheel build, they are unforgiving of uncertain wheelbuilders. Get a lighter rim strip and stick to brass nipples.
The offset does indeed indicate left and right side spoke holes.
I would read sheldon brown's brief and excellent online wheel building tutorial. Again.... Google....