The Latin-Centered Curriculum

Hello! I'm AmyBeth, mom to six kids ranging in age from 9 years to 17 months. We've been using the WTM approach and will be switching to a more Latin Centered approach next fall. Now, after reading Drew's book, I know to just meet my kids where they are at, so the both the 5th grader and 3rd grader (07-08 school year) will be starting Latina Christiana in the fall. So far, so good. Now, as far as classical studies and modern studies are concerned, I'm a bit lost. The younger kids I can start with the plan in the book. It's the 5th grader I'm concerned about. Should I just do the 3rd grade studies with him as well? Should I double up a little somewhere and have him do both Greek Myths and Famous Men of Rome in the same year? I think I want to make sure we're studying the US Civil war the same year we study the Roman civil war, so do we do that and not worry about the modern studies that go with Greek Myths year? Or should I just keep him on the 3rd grade track and just be a few years behind with him and adjust during the high school years?

Thanks!
AmyBeth