
A perennial that provides solid advice on all aspects of personal finance and investing.
What it did for me was inoculate me against all manner of foolish choices that I probably would have made during my young adulthood.
It's short, entertaining and practical. The mechanics of investing have evolved considerably over the years, but the author has released frequent updates. Also most of the lessons are timeless.
If I could sum up the most important point in the book, it's that in investing and finance, playing not-to-lose is unreasonably effective. Playing to win is usually a losing strategy.
Poland by James Michener - or any other of Michener's historical fiction. Not all of them are great literary works, but because they span thousands of years, they caused me to start thinking generationally.
Here is what I would personally suggest, having encountered a similar scenario once a long time ago...
Find a place to park about $4.9M in a CD, Money Market account, or similar ultra low risk location. Don't get too hung up on getting the absolute best interest rate, just find a place that will give you easy liquidity (ie: DON'T make a 5 year investment right now).
Then, buy and read the following books: "A Random Walk Guide to Investing" - Burton Malkiel "The Only Investment Guide You'll Ever Need" - Andrew Tobias
(and/or any equivalent titles that catch your interest).
Then once you have a good/better understanding of financial investments interview some financial advisors and talk to them in depth about how they plan to manage your assets. Ideally you're looking for something more along the lines of a "wealth manager" vs. a financial advisor.
Killing a year finding the right investment approach while your money makes even a very low percentage rate is, for a 20 year old, a better approach than rushing out and making possibly a bad investment that incurs a big loss, or has tax liabilities you don't fully understand.
In the shorter term, you should find a good local CPA-for-hire and make sure you understand any possible income tax issues. In some (many) cases, if you will owe a large income tax return you will need to pre-pay or make estimated payments. Not doing so can take a big bite out of your ass later (ref: portion above about keeping funds semi-liquid).
BTW, congrats on your success. Take it slow and don't be tempted to believe you know what you're doing or can repeat this easily (learned advice ;) ). You have much time and luxury to plan your next move, and no matter what anyone tells you, you are not missing out on the investment opportunity of a lifetime in the next 24 months and do not need to make any rash decisions.
At the same time, you should sort of off-handedly tell family and friends that you locked in to a great investment and in 5 years or so will be able to access some of the funds. This proactive approach is better than having to say no to all the outreaches for "help" and "personal investments" that tend to come with a large chunk o' cash.