5) What is the difference between the Swap and Exchange on TrustWallet?
Pretty much as you've said. Also, the swap function has limited pairs available on it. There's more info on their website here:
https://community.trustwallet.com/t/how-to-trade-with-the-built-in-dex/1696) On the Exchange, what happens if I enter in something ludicrous? I.e. Sell 1 BTC for $50,000
It would sit on the order books indefinitely until either you cancelled it or BTC hits $50,000.
7) What about is the supply is higher than the demand? Imagine hypothetically there 10 people on the exchange are trying to sell 1 BTC at £8,000 but there were only 8 buyers. What happens to the last two sellers who don't sell?
Again, you are correct. If 10 BTC are up for sale at a given price, and 8 BTC are bought, then the other 2 BTC will remain as open orders. The people who placed that order can leave it and wait longer, or cancel it and place a new sell order at a lower price if they wish.
8) If the above is correct, then does that mean the market is not immediate? I.e. Say the BTC is freefalling, and I want to sell urgently. If I put a sell position on the exchange, I have to wait for someone to accept my offer? Does that mean it would be better for me to use the "Swap" function, even though it charges a transaction fee?
People trading on an exchange in this way don't accept individual offers from other people. They just tell the exchange "I want to buy/sell at $X,XXX", and the exchange fulfills the order if there is a matching sell/buy order at the same price. If you place a sell order at a price lower than current highest buy order, then it will be fulfilled immediately.
9) On Coinbase, hypothetically, say I sell 1BTC at the market rate of £8.000, but I am one of those remaining 2 people in 7) above. I.e. there are no buyers. What happens?
what you've answer to this one is incorrect. If you place a sell order, and it isn't immediately filled, then it simply remains open until it is filled. Coinbase do not buy it and do not assume the risk. You still "own" that 1 BTC until you either cancel the order or someone else buys it.
10) When I transferred my BTC to TrustWallet, it became BTCB BEP2. Do I actually still own BTC?
BTCB BEP2 is a Binance issued token which is pegged 1:1 with BTC. No, you no longer own BTC, you now own Binance's pegged token.
Someone else will need to answer the other questions for you - I don't use centralized exchanges or Trust wallet, so I can't talk to the specifics of using them.