Number two isn't really important and I don't see it as part of the basic knowledge of bitcoin because getting a good wallet that is an open source and self custody can be a problem to a new investor since bitcoin wallet is technical. Since he is a new investor who wants to start his bitcoin investment with weekly DCA, he is to only open an account with a reputable exchange, buy bitcoin through p2p and leave his bitcoin in the exchange for the main time, while he continues to learn more about bitcoin and which wallet is best for him to use.
It's also important that when accumulating bitcoin, we don't buy bitcoin of $50 and send immediately to our self custody wallet in order to avoid many small small UTXO, which can suck almost all our profits in future if transact fees becomes very high. Good UTXO management is important as a bitcoin investor which is why you need to accumulate your bitcoin to a good amount up to $500 and above in your exchange account before transferring it to your hardware wallet.
I also think so. It is better to buy through P2P by creating an account on a good exchange and verifying it. It is better to adopt the DCA method. You can buy weekly or monthly amounts of $20, $50, $100. It is better for traders to wait for the market to fall but not for holders. After buying $500/1000, you transfer your high security to a wallet. I created a wallet, saved the phase well, kept the wallet address, deleted the wallet and only transferred bitcoin from the exchange to that wallet address and I think this is safe and good. And I wrote the phase of that wallet in a diary and told my wife because if I die, she can find them.Because a few days ago a boy in our village died. He held Bitcoins like this but we don't know his wallet phase so they couldn't be saved anymore.
Anyhow an investor is using to buy his or her Bitcoin whether P2P or not, so long as they are familiar and okay with that method and it is not disturbing them, then is good. The most important thing is that you are buying and you are holding for a long term but saving your wallet address and deleting the wallet from your device doesn't sound good if you ask me and better still you can hide the wallet in your device if you have an application instead of deleting it and lastly, no matter where you save your seed phrase if you are not careful someone will see it one day.