It looks like you're in talks with Puzzleaddict, that's awesome!!
I don't really want to disrupt your conversation with her and possibly cause confusion, but would like to offer an idea to try, as it wasn't mentioned in your troubleshooting post.
It sounds as though the problem is not so much you can't download mods and/or CC, it's that it won't install or maybe show up in game?
If that's so, have you tried creating a new Sims 3 folder?
You can do this by moving your current Sims 3 folder to your desktop. Go to Documents\Electronic Arts and right click on the Sims 3 folder and select Cut. Then go to your Desktop and select Paste. Optionally you can rename this file, by right-click select Rename. I usually rename my folder something like Sims3-Current
To create a new folder open up the launcher and then close it. Look in Documents\Electronic Arts to see that there's a new Sims 3 folder.
Create a new Mods folder, and add the Resource.cfg file to it.
Sims 3 - Creating a Mods Folder/Installing Mods Step by Step Guide
https://www.carls-sims-4-guide.com/forum/index.php?topic=9187.0Start adding your mods and custom content back a little at a time, in small batches to make sure things load okay. Test with a new save file. Quit without saving while your testing out the mods and cc.
If things aren't working, stop to recheck the batch of CC or mods you've just tried to add.
Repeat this untill you've got all the working mods and cc added back in.
If creating a new Sims 3 folder works, don't forget to let PuzzleAddict know.
Hope this helps!!