you can say: ni zhen piao liang.

Ni zao!

Ni shi dou piao liang.! dui? hehe

bu cuo, ni dong de hai zhen duo ne.
good, you understand too much, or you understand it very well. ( I prefer this one)

wo shi peng you- it means i am a friend.
But i don't think that we speak English in this way.
I would like to make friends- wo xi huan jiao peng you.