How to set up membership & payment functions Thread

I'm not a developer, but I do want to invest in a new online gaming platform targeting the preferences of older people who may (due to Coronavirus) be isolated or subject to social distancing. My problem is that whilst I fully understand how to pay to get a game developed, I don't understand who to talk to create the complex administration functionality that is normally handled by a gaming platform (like "Steam"). I'm talking about things like membership payment processing, access rights provisioning and the administration of membership lists (who is registered with the platform, who can play a particular game, who is active, and how players can find other people to play with). Platforms like "Steam" seem to handle all these administration tasks within the platform code - with an API handling the flow of information to and from each game. My question is this : if I wanted to find a specialist developer capable of developing a new platform (like a simpler version of "Steam"), then how would I go about finding one ? What skills might they have ? And are there any development tools or templates that make it easier to develop an online gaming platform ?

Your advice would be much appreciated !