So, just so that I'm clear here, I'll summarize (in case anyone else wants to know this):
If I wish to install CM, I need to create a bootable uSD card with the image I want. Once I've done this, I can boot directly from this image. If I choose to do this, I do not need to root or modify my NC. Should I wish to return to the original firmware because my NC dies or whatever, all I need to do is pull the uSD card out.
If I do this, I will have access to the remaining storage of the uSD card, and the /media slice on emmc.
The only media/B&N content that I will not have access to will be that content which requires the original NC reader. Pretty much everything else will be better - I can overclock the NC, have access to normal GApps, bluetooth access, Youtube, Flash, games, etc, everything that having CM gives you.
Using the uSD for booting means I will not be able to swap the card out while the NC is running, and is really the only thing I'm giving up here.
Please feel free to correct me where I'm wrong here, and thanks to everybody for the answers.