I understand your concerns and agree with Karen in that WTM gives you the whole bananas in one book, but not even Susan Wise Bauer says she follows it to a T every day (and didn't when she was homeschooled herself). However, I have to say, 98% of the suggestions in curriculum/methods I have found are nothing short of excellent if you desire a classical education. Each time I have entered a new stage with the kids (unknown territory) I have started with WTM's suggestions for texts, etc. because I have come to trust their brand of excellence.
We started out, 7 years ago, with your oldest in a Classical school for Kindergarten. It was a wonderful school, however, I saw in the upper grades how rigorous it really got for them. We wanted rigor, but also wanted our kids to be kids, and therefore decided to do it on our own. So, I have chosen to scale back in some things each time I can tell it is too much. I really appreciate that control. My 7th grader does a solid 6 hour day of work every day. If he were in the regular Classical school, he would also have 2-3 hrs of homework a night as well.
The hard part is that it takes a few years to experiment with time/child to see what is too much and when you can challenge more.