How to estimate scaling up costs of a project?

Question

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?

Answer 1

I think there are some fundamentals you're missing about app development, product development, etc.

I recommend getting familiar with something like Lean methodology (https://www.interaction-design.org/literature/article/a-simple-introduction-to-lean-ux) to understand how to get your idea off the ground, where the effort should go, etc.

Investors typically want to see products, data to show their popularity, monetization model, and an explanation of limitations that can be addressed given more funding.

Also, I wouldn't assume it takes hundred or thousands of developers to support an app at scale. For example, WhatsApp only had 50 engineers at acquisition time for 900m users https://www.wired.com/2015/09/whatsapp-serves-900-million-users-50-engineers/

Answer 2

Let's split your question into several pieces;

1. Startup costs: You put a budget and try to fit into that. There's no math behind "how much minimum budget is needed for my product idea?". Scrum is there because we can not answer these kinds of budgetary questions.
2. Scaling the product: You can read about high-load web/mobile application architectures on the web. You can even find the software and infrastructure architectures of Facebook, Twitter, and Netflix; they like sharing these.
3. Attracting The Investors: Co-founders are interested in ideas, but investors want to see a working product with a user/customer base accompanied by a growth strategy with a budget & timeline plan included. That's something I have no recommendations for you as a technical person :)