3. Retail Investors and GBTC: Yes, retail investors can trade GBTC. You don't need to go through Grayscale directly to buy it; it's available on several trading platforms.
4. Grayscale and Real BTC: When you buy GBTC, Grayscale uses the money to purchase actual Bitcoin, effectively backing the trust with real assets.
#3 and #4 contradict each other because #4 is not accurate.
#4 should should say that a person can deposit bitcoins into the trust and receive newly issued shares in exchange, and that Grayscale manages that process.