all you need to know, if you have 2mb connection with at least 256k upload then you will be fine as long as you dont download torrents or something at the same time, as far as bandwidth for game usage is, well thats kind of hard to measure because, it depends on how long you play the game for, and how many games you have which you play online, also calculating latency is sort of futile too, unless your playing within the country of origin, latency can not be controlled and in most cases is pure luck.
so my answer to you is, if you have 2mb down and at least 256k up you will be fine, and bandwidth usage well if your that worried about it, turn off all your pc's when playing on your wii as they will eat your bandwidth too.