I haven't needed a professional financial advisor before but for those who have received an IPO windfall in the past, how did you prepare from a tax and financial planning perspective?
I was in the same situations not long ago. Here's what worked for me:
1. Understand your tax situation. You probably have to start pre-paying federal and state taxes, maybe even in the year the IPO happens. You don't need to prepay exactly the right amount so you can just guestimate to start out, but it's good to get within 10% of the right amount so you don't pay too many penalties. Finding an accountant now can be helpful. Don't stress too much about getting it exactly right! Yes, it's a lot of money, but you're still in an area where a standard accountant and normal advice still helps.
2. Choose the schedule you're going to sell your stock at, and where it's going. I sold my stock on a regular cadence as soon as I could, which was a great idea because having 99% of your net worth in a single stock isn't great. I kept a 5-10% cash cushion, which I'm holding onto until the current economic situation seems more reasonable. For the rest, I put 80% into an S&P 500 index fund and 20% into total bond market index funds.
3. Don't add any expensive hobbies for at least 12 months.
I'm extremely happy with the results. It resulted in good financial gains, low risk, and an extremely low level of effort. I do not think a financial advisor is useful at mid 7 figures (though to be honest I didn't even try one). I was glad that I had an accountant, because taxes are where you can really screw things up (if you're better at paperwork than I am, it's not 100% necessary).
If you wanted, you could try to perfectly optimize everything and get a financial advisor, or try to squeeze money out of a variety of things like real estate, specific stock, bitcoin, whatever. But you don't have to. It's a lot of money, and for most people it's enough, so index funds are good enough to get some additional value, and then stop worrying about it and go back to thinking about the things you'd prefer to spend time on.
You question is general and has no focus, so you should get a tax and financial advisors to help your specific case. Remember spend $ to make $$ :). Talk to someone trusted on this