Honestly this is mostly bad advice. The guy should just sit on his hands for a year or two while he processes the idea of having money. Telling somebody who has never made a big financial decisions to start buying millions of dollars worth of financial assets is terrible advice. Unless by "start small" you mean invest a non-material amount, which still leaves the question: what to do with the remaining 99% of the money. My answer: nothing. Checking/savings account is fine.

When you have a large amount of money the most important thing is not to make any huge mistakes. The best way not to make a huge mistake is to just sit on your hands and do nothing. This is advice that anybody can follow, as opposed to your advice which is vague and absolutely not without risk (there is nothing conservative about buying index funds 10 years into a bull market).