if i have a usa game or wiiware, can i play online with the japanese?

Yes you can play online with the Japanese.

Yes it's free to play the games online.

I haven't played many online games on the Wii but for the ones that I know are international there was no way you could chat to people. There are probably some games where you can do some kind of communication.

it all depends on the game. like for instance i dont think you cant play people in foreign countries in super smash bros. brawl

Yes, usually on Wiiware games it will offer international servers, in which you can face people in Japanese.