I have figured out how to play the sims 3 on Mac after all this time!!!!! And I only think it's fair to share how i did it after copious amounts of research.
Mind you, I am not as good as explaining things so bare with me.
1. So first things first, go to origin and download Sims 3. If your Mac does not run on 64-bit DO NOT download 64-bit because it can become very confusing.
To check if your mac is 32-bit or 64, click the apple logo in the top left corner, go to 'About This Mac', then click 'System Report', go to where it says "Graphic/Displays" and it should say it under pixel depth. Now, this could be different for other versions as I have a Macbook Air from 2013. It is MacOS Sierra.
DO NOT INSTAL PACKS YET!!
2. After all the installation is complete, start up Sims 3 to make sure it's up and running good (go to CAS, or simply start playing a random household). I never had issues with starting up The Sims 3, so if it doesn't open, I'm sorry.
If you're only playing base game, you're good to go & scroll down to the end of this post to see some things you should be wary about when playing the sims.
3. When The Sims is running good, you can then go and Instal your packs.
4. When Installing Multiple Packs then trying to run the game, you will likely get 'Unexpected Error' or something like that. I found a really good solution: https://answers.ea.com/t5/Technical-Issues-Mac/CURRENT-ISSUE-Sims-3-Unknown-Error-in-El-Capitan-and-later-OS/m-p/5794065
if you scroll down a bit, you will find a comment by @corey_0414. They explain a method that helped me fix my game. So read carefully.
For University Life players, I'm almost certain you will not be able to play that expansion. The game quits by itself because of how much Memory the world uses up. And I'm pretty sure it's the same for Island Paradise but you can test that out. (This is my experience with University Life)
5. Try running up your game. It will take about three to five minutes for the Launcher to open (from someone with only 3 expansion packs installed) and it should work fine.
Here are some Issues Mac Players will run into.
Your time in CAS is very limited. I would recommend spending 10-15 minutes in CAS because of how much memory it uses. Though, it's fine for me to get in and out of CAS, creating different households.
In my experience, I could spend about 30 minutes to an hour in Build/Buy Mode. After you get out of Build Mode, SAVE UR GAME IMMEDIATELY!! I cannot stress this enough, I had to redo so many plots because i forgot to save after building. And sometimes after getting out of build mode, about five minutes later, my game would quit so this is why.
I would say you would get to play around two hours until your mac gives up and the game will quit on it's own. So occasionally save your game. especially after important events.
Be careful of what CC you install. I would say make sure you only put .package/.sims3pack files and avoid putting in .rar/.zip files (break them down first). If you have bad CC, the launcher won't open.
Mind you, your mac will get really hot so have like an ice pack or something under it.
This is all I can think of so far and my experience with Playing the Sims 3 has been satisfying to say the least.
I AM NOT a professional at this stuff, just a fellow simmer so I may not be able to answer certain questions. I hope this works well for you.
