There is medical condition that affects someone close to me that I’d pump a shit load of money into researching, seeing as nobody is really funding it. That would be my “selfish” good deed.
I think I’d buy Southend United and invest a shitload to get them back in the football league and then hopefully swiftly up the divisions. Fuck any other small club that tries to stand in my way. Don’t think I’d touch Arsenal with a bargepole, even as a carefree billionaire I’d rather not have Arsenal twitter on my case. Going for a vastly smaller club I have a fledgling connection to seems much more my speed. The lower starting point means it would be far easier to get to a point where I’m considered an absolutely bloody legend for what I’ve done for the club.
I’d pay off all family debts, mortgages etc. Offer to buy better houses for anyone who wanted one.
And like @shamrockgooner I’d like to do something big to help with homelessness, as that’s one of the causes I care most about.
I’d probably then invest anything left into pioneering research into new drugs that are totally harmless and non-addictive. If there’s nobody out there researching this then there soon will be when they see what I’m paying.