It seems strange to cap the number of shares, which makes me wonder if this is the number of shares in an option pool. If so, nothing can be inferred about percentage ownership, except that your friend would likely own a very insignicant number of shares. Note that a new company typically allocates 10M shares, so it's additionally unclear why now there are so many.

This is incomplete information. Shares will be limited in what context? Employee option pool, this round, ect.

As far as I know, early-stage companies don't put an upper cap on the number of shares that can exist in the future. Is this some sort of crypto company?

If you believe that valuation then it's ~$1.5M over 3 years. I would personally ask for explanation of the $70B valuation because if it goes for a piddling $500M your friend gets ~$11K over 3 years

This is impossible to guarantee. The company may need to raise more money, likely through equity, not debt. To issue more equity, they will need to issue more shares. That is just how it works.