That's awesome, congratulations!
If you're not already familiar with FIRE (financial independence, retire early) then check out these subreddits:
* http://reddit.com/r/financialindependence
* https://www.reddit.com/r/fatFIRE
Most people use a safe withdrawal rate of around 4%. If you retire at 50-60 and invest your money in index funds, you can withdraw around 4% per year if you want to end up with $0 just before you die. If you use a much more conservative rate of 3% and minimize your expenses during a market downturn, then your assets should actually continue to grow while providing you with a steady annual income.
$8,000,000 * 3% = $240,000 per year
So the first thing to realize is that this does not make you ultra-rich. There are plenty of people working at tech companies (especially managers) who are earning around $240k per year. However, this means you can earn the same annual income without ever working again for the rest of your life. Don't buy a bigger house or a few new cars before you think about this carefully. It would be very easy to inflate your lifestyle or send your kids to much better schools, and then you would just have to keep working to pay all your bills (and you probably wouldn't be any happier.)
I don't think you need to hire a financial advisor. $8M is a lot of money, but it's not too much to invest by yourself. If I were in your shoes, I would put a lot of the money in index funds (VOO - Vanguard S&P 500).
Also you should really ask yourself if you need more than $8M, or if $240k per year for the rest of your life is plenty of money. If so, I would avoid any risky investments, because you need them. If you want to do some angel investing or buy some Bitcoin, do it with no more than 5% of your assets, and just because it's fun. Don't purchase any rental properties unless you want to deal with maintenance and tenants. And definitely don't be tempted to start your own company and invest a lot of your own money. You would be taking on a huge amount of risk for no reason. It's very easy to lose all of your money that way.
Anyway, I should try to answer your questions:
* Should I donate it?
Yes, that would be great. If you want someone to recommend numbers, then I'd recommend an initial donation of $1M, and then 10-20% of your annual investment income.
* Should I hire a personal wealth manager?
No, I don't think that's necessary. A lot of them end up charging really high fees for below-market returns. I would start looking for a good financial advisor around $25M. But you should definitely find a good accountant.
* Should I retire?
Yes, definitely. At the very least, find some work that you enjoy. Don't just keep going into work because it's what you've always done.