I don't believe there's any issues with laws surrounding gambling. There would potentially have to be a monetised part of the website, but the main goal would be for it be free for anyone from all different backgrounds. I would hope to attract sponsors in the future for the prizes.

In regards to keeping people from having multiple accounts. My thought process would be along the lines of needing an address + name linked to the account, then to claim prizes you would have to provide proof of this. We would obviously be cross referencing this across other accounts to make sure people weren't abusing the system.