2. Investing money you cannot afford to lose
I can not do this with altcoins but I can do it with bitcoin. Although, not a good advice for newbies.
8. Investing in Just One Type of Crypto
If the coin is bitcoin, why not? It is good like that. But, if the coin is altcoin, I think people prefer to diversify because some altcoins can fail to rise during bull run.
If you want to look at it from a different perspective, and when I say this I don't mean to say that this will continue like this, but anyone who invested, and then at least held for 2/3 years profited massively, and not one of them lost money.
It depends. If it is bitcoin, I agree. Bitcoin all-time-high in 2017 was $19650, but its all-time-high in 2021 was $68900. Their were many altcoins in 2017 that has not reach their all-time-high in 2020/2021 bull run. Example are ripple, bitcoin cash, eos, qtum and many others. They may still reach all-time-high but it is getting far unlike bitcoin.