4. When people buy GBTC shares, the money they spend goes to Grayscale. Grayscale then uses some of that money to buy real Bitcoin. So, yes, they use the money they earn to buy Bitcoin. It's like trading your toy money for real toys.
That is not true.
Or better, you have to specify.
If you are an accredited investor and can access the primary market, then the above statement is true.
If you instead access the secondary markets, the one usually accessible to common investors, then you are trading with another shareholder, Grayscale is not involved in the trade, so the money goes to the shard seller.
Please note that the primary market has been closed for a few years (it' wouldn't make sense to open it with a negative discount on the secondary market).
Again all this is explained I'm my thread.
Edit: While typing I saw this very good reply:
That is not accurate. When a person buys shares of GBTC, the money goes to the previous owner of the shares. However, when allowed, a person can also deposit bitcoins into the trust and receive newly issues shares in exchange.
Indeed, when the primary market is open you can either deposit cash or deposit Bitcoin (in-kind purchases) to buy shares.
But again, this possibility has been closed for a few years now.