The rest of the questions come down to the third question - the size of the folder that has been set. It is the overall folder size limit that will control how many files you can upload.
In CA PPM On-Premise, you can configure this setting yourself. See here for a screenshot or here for the CA PPM documentation.
Top of my head, I'm not aware of this folder size setting for a CA PPM SaaS customer. If you don't get an answer here, please log a CA Support issue and we can check the setting directly.
Another way of thinking is to rephrase the reverse questions:
"How many documents and how much space do I anticipate using?"
Most sites (I guess) won't be anywhere near a practical cap if adding a large number of small documents, or a regular number of medium size ones.
Thanks, Kyle_R.