It sounds like you're ready to start working on OG, yes.
Note this: Most of your learning will come not when you're doing the problems but after you're done, when you're analyzing them and figuring out what you need to get better at for next time.
Here's how you do that:
http://tinyurl.com/2ndlevelofgmatAnd, yes, you're going back into your strategy guides, or any other resources you have, when you discover that you've got a particular weakness that you need to improve.
Let me know if you have any questions about the 2nd Level stuff. Then try it out and tell me how it's going.
(Expect the analysis to be slow / take time at first. You'll become more efficient as you better learn how to learn from these problems!)