For Mac and iOS:
There is no limitation in number as well as size of the files you can store in the Safe. The only limitation is the available space on your advice for the Safe itself.
The “Secure temporary Storage” (Mac) is necessary for preprocessing and editing the files (read this article about the “Secure Temporary Storage”).
The size of the “Secure temporary Storage” is limited to 500 MB for the Mac App Store version. See also this article about the differences between Apple Mac App Store and Non-App Store Version.