How many additional numbers can I set in one contact? How many additional numbers can I set in one contact? 

I was playing around with a script and I was able to get only 400 of them in on a simulator. However, I would like some official response about what is the maximum, and does it vary based on the Android version.
Clarifying on your comment asking for a rough estimate, it is 499 and that seems to be not rough but pretty much fixed . Source- from SE webapps- What is the maximum number of phone numbers per one contact in Gmail?

It is relevant in the sense ultimately your contacts are going to be synced using Gmail , while the Android capacity may be more or less, it doesn't matter and by the same logic Android version shouldn't either