Is co-op playable through the whole story mode like GoW style were u and a friend can just go through everything together or is just certain parts are co op like GTA style were its just you two going around acting crazy?

Its GTA style.  There is a saftey that the host has that prevents the other player from killing civillians in his story, he can turn the saftey off if he wanted to though.

I believe, it's the entire game that you can go through, but while I think about it, I don't know how the child hood would pan out with co-op.  So it's my guess that the co-op will become available after you are done with childhood which seems to be an hour long of gameplay.

You can play the entire single player in co-op and you can do all of the jobs; you can even get drunk together.
This is not going to be as lame as GTA.