I think we can use it for even bigger investments. if we immediately spend it, it will only be wasted. we take advantage of the moments where we get great capital and we start to invest even more.
I think you should really consider doing it legally because it can cause you many problems in the future, especially if the number will reach millions. and depends on where you are, but generally it will be easy if you just convert your crypto into cold cash with a face-to-face meeting. It will be difficult if you need to transfer it to the bank and trigger a sort of AML or contact your government about it. Only under the radar through methods that cannot be tracked like cash.
In my opinion, I think having million worth of fiat transaction is difficult for you to cash it in just a day or two. Maybe it is better if you would do it gradually, just enough amount in a day or a month, an amount that will not cause any suspicions from other people, or even from the hackers. When you get the fiat already, consider putting it in a bank gradually also or invest in in real estate or business.
its like a money laundry but after all i think its legal money, i just afraid with goverment to steal what i had been earn for a years. 
