The Sims 3 Installation

Hey, so I created this account because I need help installing TS3 on my Imac. 
I have your guide up, but I haven't even gotten to step one in that guide yet. I downloaded the complete collection instead of just the base game, because the link wasn't working anymore. But I can't open up the base game. The guide says I have to open the setup.exe file, the program recommended to open it is unarchiver, but it wont open. 

So first of all, how do I install the base game? 


I tried an alternative way, I downloaded another collection of TS3 games, the one with dutch titles. I can open the TS3 launcher, but have no idea what to do after that, as there is no installation guide. Do I apply a crack? And how? Also, not all expansion packs came with this collection, so is there a possibility to add more of the expansion packs to this version?


I reckon there are many threads like this one, so if there already is a one that answer my question just link me to that thread. You can also PM me the answer if that's easier.

The error messages that comes up when I try to run the game says "No game disc found! Please insert The Sims 3 Showtime game disc before proceeding."

I have downloaded different versions of the base game, the one that opens already have all the EP's up until Showtime, so it seems to be the one from "The Sims 3 Complete". I'm trying to work out how to open "The Sims 3 Complete Collection", the one I downloaded from here. But will this version with showtime be in the way? Do I have to delete that file?



Edit: I have a new problem with the Disk Utility process, I can't seem to create a .dmg file large enough? I don't have the costumize option, I can just write in the size, but it doesn't create the correct size. I write in 6,07 GB and it ends up being 1,5 GB. I wrote in 6070 MB (because 100 MB is the default) but I got a 1,7 GB .dmg file...