If you are using the Aspyr Mac version, the file limit is 12800 total. Maybe a few more, but not many.
If you are using Windows 98, I have experienced a similar limit that causes a crash when exceeded.
Under Windows XP on an NTFS partition, I have had over 25 GB of files in my user folders without issue - yes the game was slow to load, and all, but it worked ok after loading, but I have 16 GB of RAM and dual CPUs, I dread to imagine what would happen on a smaller system.
Under both Mac and Windows, there can be problems if you have excessive sub-foldering. In this case the length of the address can be the problem. For example:
C:\Documents and Settings\Sasha\My Documents\EA Games\The Sims 2\Downloads\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolder\subfolderis just begging for trouble. I would be surprised if the hard drive would even accept such a set-up without serious problems.
I have seen drops in performance at fairly regular intervals:
- 8192 files
- 16384 files
- 24576 files
- etc
I had a game failure that I could not correct until I reduced my downloads below 32000
But the game will have trouble when you have too many screen captures in your Storytelling folders, no one has been able to give me a figure that is the limit there.
The same is true of the SavedSims folder, different people have reported problems when they have more than 100 Sims.
As for collections, I don't know. Some people have the game crash if they have even one user made collection, others have 100s.