I'm not sure what uninstalling and reinstalling would do to the ccmerged file; but, hopefully, as you say, the newer would just overwrite the older info. Nonasims offers info and a link to her ccmerged file, if people have problems.
https://nonasims.wordpress.com/2012/05/17/dcbackup-ccmerged-package-and-your-premium-content-items/
Once you've done the complete install, the dccache folder will have all your store content in the .ebc files. The .dbc files in that folder are for cc or what your game perceives as cc after downloading through the exchange or elsewhere. The dcbackup folder will have all those package files of everything installed (unless you move them) as well as the ccmerged file that you need to keep there. The venues and any sim or lot you install will create a library file if it goes in the bin or a savedsims file if the sim was shared in CAS. The installed worlds create a .world file, as you've already noticed in the installedworlds file. Once you play a world, it then also creates an object and sims file in the worldcache folder, but that's just a cache, so I believe that the game will just create these fresh when you choose to play a world.
So, those are the important files to backup along with any save files you might not want to lose (after you start playing). You might also save the options file as it would keep you from resetting the options the way you like when you start as well. (It's where you tell it not to save memories or show store sales or what weather you want to turn off, etc.)
Personally, I just copy the whole sims 3 folder when I finish installing to a safe location outside the EA folder; but to save space you could just copy the key folders.
I always use "save as" to save a game and give it a name based on the in-game time. So, SV-Skmt-M1630 would tell me I'm playing in Sunset Valley with the Sekemoto family and it's Monday at 4:30p.m. in game.
I'm glad the spreadsheet makes sense to you now. Good luck!