Thank you very, very much for the idea. I set up cmd.exe as an executable within MO, then used the command:
Dir /a/s on the data folder in MO and it looks like I'm using about 60.966641938 gigabytes, which is about right:
Total Files Listed:
386111 File(s) 65,462,433,318 bytes = 60.96GB
C:\Games\Steam\SteamApps\common\Skyrim\Data>
The MO mods folder shows 68.9 GB (74,022,482,501 bytes), 421292 files when checking its properties outside of MO. With all the overwrites the net result would naturally be less, so this all makes sense. That MO mods folder includes all the bsa & esp files from the base game and DLC's too, as I converted them to 7zip files and pulled them into MO as separate files, each one treated like it was a mod. Skyrim.esm and Update.esm are the only plugins that actually remain in my native Data folder outside of MO. What I like about that is MO tracks pretty much every file and lets me know if a mod is overwriting a texture from the original skyrim textures, for instance.
Again, thank you. I just started using MO in the last couple months, and it is nothing less than outstanding.
Edit: I probably should have mentioned I've expanded all BSA's, so everything is unpacked and ready to go when the game has to load something.