You've pretty much got it. In terms of the BC, C7 is only used in Stage 5 blues songs. However, it's a very useful shape to have in your arsenal, so don't skip it. Since Stage 5 is dominated by Blues, I think Justin moved some of the 7th chords down to Stage 4, so as not to overload Stage 5 with too many new chords.
In general, as you get to the later stages of the BC (5-9), you'll find that the songs don't align with the new chords as well as Stage 1-3. This is even more so in the IM. In terms of open chords, once you have A,C, D, E, G, Am, Dm, Em, B7 down you can play a lot of songs (especially with a capo). The addition of F and Fmaj7 completes that. Also, Bm would be nice to have though Justin doesn't introduce it in the BC. Most of the additional chords will not be as prominent. You're going to play D and Am the rest of your guitar playing life. C/G or Am/G (Stage 9) less so.