Backend Coding for Website Community Game

I want to design a community type game based off many forum games. It is going to be a "Survive until the end type of game". Basically, 20 or 28 people will form 4 tribes (5 or 7 per tribe to start the game). I will submit challenges and the tribes will get a certain amount of time to answer these and submit. After scored, the losing tribe will vote someone off, until there is a winner. This is a basic summary but I will be willing to work with a company for all the further details. I think the site would best be done in PHP. With In game chat for all players, "Tribe Chat" for tribe only. Challenge button where players will submit their challenge entries... and also voting blocks where they will submit votes for elimination. Also private messaging would need to be installed. If we had 500 people sign up, technically 25 games could be running at once... with the same challenges, but amongst different games..... I put a basic idea on how user dashboard would look. Of course there would be a backend dashboard where admin could submit different challenges... score the previous challenges, and announce winning tribe or losing tribe. Losing tribe would show up RED and Winning Green, so losing tribe would know it is time to vote. More details to come, but I'm hoping to find a backend programmer to work with me on this project.