Ask HN: To start a freelance market place like upwork

I have an idea of starting a freelancing market place like upwork.com/freelancer.com with a different approach.

I would like to understand the process of mediating the money transfer part between client and freelancer. Basically, The market place maintains an bank account which charges to client and transfers to the freelancer? How should the startup should be registered with the govt agency, as software company or any other entity type?

Any site where I can get more details about the process would be appreciated