You never need go into the purchase history! Save that as a last resort!
Valgon has made threads and spreadsheets with direct links to almost everything. I included his data in my spreadsheet (with permission).
So, if you use one of his direct links and you get a negative response, it's because that isn't the version you need. It doesn't hurt to try all of the links, if in doubt. I should have his info linked in my reinstall thread which is linked in my siggie.
That said, you probably saved all your downloads somewhere, right? So, even if you end up reinstalling to get the configuration you want; you don't need to redownload.
If you never deleted items out of your DCbackup folder, then, yes, EVERYTHING you installed through your launcher is backed up. The problem - it's all just a bunch of numbers which leave you guessing what's actually in them AND you really don't need anything hanging out in there. It's said that you need that only to ensure that your data will be transferred during uploads. I've had everything transfer fine without it. I think though that some things are tricky when the game sees them as cc. For example, some venues install with the cc tag instead of the store tag. (I have no idea why as sometimes they install as store icons for me and sometimes they don't - and yes, I bought them all - but maybe I installed from my PC rather than the store!) So, if it's not venue-related and it's not cc, I wouldn't keep it EXCEPT as a backup somewhere other than my sims 3 folder BECAUSE these files can be put in your mods/package folder directly if you can't get them to install sometime later down the road because of a different OS or game type (i.e., you had Digital Download, but now you've switched to disc or Steam versions rather than Origin).
That said, whenever you want to create a brand new Sims 3 folder for a specific purpose, you simply rename the old sims 3 folder (so it's a backup) and once a new game is launched, you can quickly adjust the settings and save a game. Then you copy in some of your old files. You can try to update the store content file first and see if it works. If it not, you can simply copy that folder or files.
To have one sims 3 folder for building, I like the empty worlds that Flabalki has done over on MTS. You can find completely empty or those with commercial lots in place. They load super fast.
I like to keep those that I have edited to remove parking spots and troublesome fencing in a saves folder, so I can quickly just copy that save into my sims 3 folder before loading. (If you start with all the same store items and/or cc, then the save is the only folder you need to copy over, unless you need a particular library folder or saved sim too.)
If you saved a copy of your pristine sims 3 folder (which is really just like a regenerated launch, but you've adjusted settings already) and then another after you installed all your store content. You have everything you need to get started. You should then add your cc to a COPY of the store content folder. So, You have three complete sims 3 folders in a backup - one totally pristine and unplayed, one with store content added, and one with cc. I do go a step further and have a version with all the unlocked stencils. I love the mod that lets me play with removing stencils as well (velocityGrass also at MTS).
Bottom line, you can save much more than you need and end up using up all your backup space OR you can know just which folders are key. By using the same setup for all my folders, I can just copy in my store folder and start a new build. When done, the build is exported from this clean folder (HOPEFULLY) that never had any other downloads added it.
For playing you'd want your store plus cc folder as a start and then just copy in the save you are playing at the time.
