If you want to diversify your portfolio, better to diversify trough other investment not crypto space e.g. real estate, stock, gold etc. This will prevent the risk if crypto market goes unhealthy.
I agree with what he said that diversifying your portfolio doesn't mean that it is only on the cryptocurrency but other assets as well like the ones he said already as well or maybe add investing into business maybe like crowdfunding other business and the like.
As for my part, that is why I also quoted this because aside from my crypto investment I'm also investing into stock market and maybe real estate in the future. I thought of investing into Bonds as well but seeing its annual yield, I just decided to put my money into stock market (REITS in particular). But to answer you OP, since you are in a Bitcoin forum I think just focus on the top 10 coins but first at least have some knowledge because it will help you in your investment journey and it will you prevent getting scammed as well .