Actually, all of this stuff works exactly the same way on Macs as it does on Windows. And the Launcher is just as temperamental, even more so it seems on the Mac version.
You were right in that it doesn't matter how you answer the "Do you wish to debug it" question. By the time that prompt shows up, the game has really already crashed.
Sorry, but if you have any installed CC or EA Store content at all, then you must have a DCCache folder someplace. It's supposed to be in your game folder, that is the one in user\Documents\EA\TS3. Stuff in your Downloads folder is only there for the Launcher to read and potentially install. Stuff that is already installed lives in dbc and ebc bundles in DCCache as @brappl218 said. Perhaps do a Spotlight search for DCCache to find where this folder is. If you actually have two game folders going on, that could be part of the problem.
If your game folder is actually not in Documents but buried someplace in Applications or Transgaming, then that is also a problem. That's the (very) old way of arranging things and hasn't been supported since before Patch 1.12, over five years ago.
Patching (or re-patching) up to 1.67 should place your game folder where it belongs in Documents. The SuperPatcher is available here:
https://help.ea.com/en/article/the-sims-3-super-patcher
Hopefully that will help sort things out.
