Congratulations on taking the step into the wonderful world of app development. The response to your question will vary depending on each individual responding to it as each has a different view about things based on their own experiences.
Here’s my take on this.
The thing you need to build a company like square is lots of cash. The only reason that you would now need cash as compared to when Square was not build is you have a benchmark to achieve. With this cash, you can either outsource (because you are unable to find local talent that can build the company and infrastructure that you want) or you can employ a team that does it for you locally in your city.
Lastly, after you can develop what you want (which can take anything from 3months to 3 years - estimates that vary on several factors) you need to have the market, developers, etc want your product. Not having an uptake of your product, you can lose all of that investment you might have made.
So I would recommend that if you want to replicate that, you’d better start collecting some serious funding money first.