You're setting up a service brokerage for custom programming, ok no worries. Tons of them around, many successful. Also called headhunters, recruiters, IT providers, etc. Most of the companies I've dealt with have local offices and are staffed with people to help you fill a contract or job. You are going online-only, which is going to be much more challenging, because you can't send your professionals off to interview with your clients, and give your clients the opportunity to select the people that will be on-site providing the service.
Speaking of clients, is your idea to gather professionals first, then clients later? That won't really work out very well... not many programmers will wait around for work-- they'll find work elsewhere so when you finally call on them they'll be busy. Better to find clients and post the job openings which will attract programmers.
At any rate... good luck with your efforts.