What size DVD-R do I need to burn wii games and do i need Duel Layer?

Even if you successfully download them, you wont be able to play them without modding your system. Consoles have an electronic key that allow you to access the data on the disc, if you dont know how to replicate it, your console wont even recognize it. Its like trying to play a ps3 game in a pc. The pc doesnt know how to access the data because the code and the key dont match. But as far as size that you need, just put the game in you computer, copy the files, and how ever big they are, thats how big your disc needs to be at the least.