Let's say if I use a ready solution to build the marketplace, whom do I require in the backend to control those things? What job roles should I look for?
The answer is probably "it depends." What kind of out-of-the-box solution lets you do what you want? How much skill is required to make adjustments and build customized components versus just operating the built-in features? Are there any programming language or coding skills required? Is there support available from the software company? Are the functions you're looking to cover purely technical, or are there accounting, logistics, and customer service requirements?
There's not enough information to guess what you need.