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Well Elon Musk is just straight up a rich guy, so I don't think that you could just do that same thing that he does unless you're in the top <5% of "those people" in the world. Since you mentioned that there would be given resources anyway, it would be better off just absorbing other businesses out there if that's what you can call it in "buying other existing business".
Why would you create something from the scratch anyway if there's an existing of it already, say for instance the trending Musk-Twitter saga. Unless you want to spend years of research in order to create the app that would replace the current Twitter, then buying the existing the business would be better off. It would save ya time, money and also you have the control to wherever the product would go in the next upcoming years.
Buying and existing business is very risky and if you could have that chance and patient to nurture and start growing your personal business would be more better. Know this and have peace of mind, to every business there is a secret and if you buy a business you don't have the idea of or because you noticed there's much profits from that business and you think if you buys it you would also starts making such profits is something impossible, although sometimes it doesn't work that way.
It's risky, but why bother settle for a dying business if you can buy the one's that's still continuously relevant. OP even indicated that assuming you have the given resources available anyway so there's that. In that case, it would be riskier to start new ones. Let's say that here in my area there's that monolith Starbucks in the center of my city and many business owners would just build coffee shop around it. Surely most of them would just crumble.