The best thing Mr. Musk can do, in my humble opinion, is to never, ever take SpaceX public.
Don't the people working for SpaceX deserve to have liquidity?
Isn't it fair for the general public to have the ability to profit off of his epic feats?
There is a robust secondary market for SpaceX stock.
The secondary markets for private securities trade "over the counter" [1]. There is thus no singular "market" which could be said to be the most active. (If you're looking for a more-actionable response, feel free to pop up your email.)
[1] https://en.wikipedia.org/wiki/Over-the-counter_(finance)
(And I was curious whether there was anything like SecondMarket/EquityZen/etc where they're frequently traded in a more standardized fashion)
I have never ever heard of this being called fair in my life. Honestly, I would have to go with "I don't know" for this answer.
That's a very weird definition of fair. Why does the general public 'deserve' to profit off of his feats?