Keeping Bitcoin in a hardware wallet isn't the only thing to look after, the back up seed phrase/ recovery phrase and the associated private keys is very important factor for safe wallet. I saw a post on X where a guy posted an advert for any person who saw his hardware wallet, he is offering to to give the person some amount and form the look of things, he didn't do a proper backup where his funds were kept else he would have just move the fund to another safe address instead of looking for the loss wallets and his house key.
DCA is one of the best and safe way to buy Bitcoin but the problem is not everyone has free money to buy consistently as the market drop, but if OP has the cash flow to buying as we dip, it will help him big time instead of buying at a spot when the next direction is not certain yet. But emphasis of wallet back up shouldn't be underrated.
I fully agree that making copy of your wallet backup phrase and private keys is very important. Story which you mentioned about someone losing their wallet and offering reward to get it back shows how important backups are. It is surprising they did not make copy which is easy step to take to avoid stress and losing money. I also think DCA is good way to buy Bitcoin but it requires having extra money to invest regularly. However making sure to back up your wallet is crucial and should not be ignored to keep your money safe.