I think your plan sounds really good! It sound like your finding the fit that will work best for your situation.
I'm glad your son will get a chance to use Preparing Hearts. It will help him be even more productive and make more connections within CTC next year. On the plus side, it is nice to combine when possible! As far as extending goes, you have some good ideas in place already until you are able to find some of the extension pack books. The history study in Preparing Hearts is very rich (especially if you have the Basic Package for reading aloud and the Deluxe Package for your daughter). I would definitely have your son listen in on the read-alouds (which add much to the feel for each time period). I'd also have him read the Deluxe Package books and do those assignments too, even though they may be a bit on the easy side. The books are interesting in content and add much to the program.
Last, I would also make sure that you have picked challenging books for DITHR for your son as that will up the level of reading/lit. study. Then, you'll be fine.
Blessings,
Carrie
