The #1 rule that you must understand regarding software is that everything that is shipped and not properly tested by professionals is going to become a headache.
You will need a team of front and back developers to manage a software of this kind unless is a solution that you brought from a company and they provide support to the software.
#2 Don't hire cheap developers to build a very complex system that involves money, they will not follow all the best practices while building your app and you will be vulnerable to be hacked.
#3 After you build a software badly, it will become more costly to grow or maintain, you will end up losing more money than you will gain. Somehow it will need to be made from scratch.
If you need something fast, buy a tested software that has been widely tested and offers support for any bugs that will occur during life of you agreement.