Let's consider an entrepreneur decides to create a new company like Airbnb, Netflix, etc. The problem is about the software part. He doesn't know how long it takes to create the mobile/web app? How many frontend developers, backend developers, devops engineers, graphic designers, etc. are needed to be hired and work on the project? How much is their salary? How much do they need to buy/rent properties like servers, software licenses/subscriptions, etc.?
Where can he find the answer of these and similar questions? Should a project manager answer them all? If so, how the project manager collects all the information? Does he/she know these information from his/her previous experience or will he/she go and ask from other guys? From who?
I am a CS graduated and like to be an entrepreneur. I have an idea and I can write a mobile/web application for my idea. But I know it may work for only 1000 user and can't work for a millions/billions of users, because working on that scale applications need a lot of expertise and hundreds(maybe thousands?) of engineers working on it like big tech companies like Microsoft, Facebook, etc.
My problem is this huge gap between an app written by one person at home( That can support thousand of people) and an app written by hundreds of developers in a big tech company( That supports billions of people).
I don't know if I want to bring my application to an investor and he/she asks me about the amount of investment, the number of people should be hired, the costs of property we got to buy/rent, etc. what should I answer? Because I really don't know what is the process of moving from an app supports thousand of users to an app that supports millions of them?
How can I find out this?