Need advice on which time period to start with SCM and TQ

We are switching to SCM for my youngest 8 children (we have 10 children, but my high schoolers are doing something else) from another program I used for the past 3 years because I want to simplify and streamline homeschool, combine the children, and use a CM curriculum. We’ve covered ancients, medieval and early American/World the past 3 years and all of us are interested in modern times. I will have 2 8th graders, 5th, 4th, 2nd, 1st and preschool (and a toddler) next year. I am planning to combine SCM with TQ to the best of my abilities! Lol!

So my question is–if we plan to start this at 8th grade, and want to eventually get high school history credits fulfilled, would it make the most sense to start at the beginning and work our way through chronologically, or is it possible to start at modern next year and in 9th grade for my girls start at ancients. I saw TQ has a schedule if you want a 5 year plan.

Ant thoughts on where to start? Also, if I use TQ for their commentary and the majority of my kids are 5th grade and under, do I buy the younger American history guide or the older since I have two 8th graders? I don’t want the commentary to be over the heads of the majority of the kids I’m teaching, but I do want my 8th grade girls to hear the rich commentary.
<p style=”text-align: left;”>Thanks!</p>