I hope we could Buy Game credits through Cryptocurrencies or even The online games can make us buy directly with just having an address in order to buy their items directy

This is a good idea! What game are you planning to start with? Just my 2 cents, you can try with DOTA 2 as this is one of the most hyped games as of late.

You can have a tournament set up paying the 1st up to the 3rd place.

Big prizes attract many players, but for that you need to have a big event with many sponsors.

Did you think about how you are going to attract enough bitcoin as prize money? Maybe some gambling sites could sponsor the event.

What game? If that worldwide and online tournament i would happy to join.
You can buy game credit voucher using cryptocurrency although not all game credits can bought with bitcoin

successful in what sense? are you planning on selling tickets or something like that to cover the "prizes"? or are you going to pay them out of your own pocket? if it is the later then yes it will be very successful but if you plan on selling tickets or raising funds or something like that, I don't think you can get that many people interested in it enough to pay you! even with escrow since most of these games and tournaments are free. and you can always join online and play for free too.

it is an interesting idea though. you can use an escrow with multiple signatures and since everything will be on the blockchain the prizes will be transparent.