I'll answer what I can:
First, you're correct on the valuation. If they are exercised and cashed out at the IPO price, the employee would earn $80k pre-tax. However, historically most IPOs are priced to get a "bounce" on opening day also there are usually restrictive covenants around the number of insider shares that can be cashed on IPO day. (This is meant to give investors warm fuzzy feelings about the stock.) In all likelihood the employee will have to wait some more time and will probably cash out closer to $10/share.
The Pricing and Valuation implies 300M shares. However there can be many classes of stock, both common and preferred that grant different rights and ownership. If they have different classes they could have a different number of shares, but the different share types are valued differently.
Shares are just objects granting different rights around the company within certain legal limits. (Ownership, Governance, Profit share, etc.) If you have agreement from the controlling body you can instantiate, remove, or restructure shares at any time. The point is that they could have decided with their bankers that 300M was a good number of shares to have at an IPO and decided to split or reverse split as part of the transaction. It has no bearing on the number of shares today or a year ago.