My questions are below if you can help please
1. Do i do the same and open various wallets and buy the coins that way or do I have to use an exchange like Coinbase or Binance to buy the coins?
2. If/when I want to sell the coins do i withdraw via the wallets or do i go onto an exchange and sell? Then transfer the money to my bank account.
3. Is there a secure wallet I can get with can hold all the coins in 1 place or do i have to open multiple wallets?
1.You can use the same meta mask to store multiple coins since Metamask supports adding different chains. For bitcoin use electrum.
2. Generally you will get better price deals when you buy and sell on exchange than swapping and definitely you need exchange if you want to convert to fiat or you have to swap in metamask then use p2p exchange to convert into fiat.
3. Unstoppable wallet is a multi-crypto wallet available for Android and ios not desktop which is not user friendly but a lot better compared to closed source wallet like trust wallet.