About the To and For stuff, has been already discussed (and it´s open to more comments).

   As for your original sentences:   "he's very good dog for me or he's very good dog to me" I would change it a little bit.

   So, redone; it would be     "she/he is a nice dog/   I think she/he is a good dog."  (it implies that it is to my thinking)

   I don´t know why, but a dog "being good for me" personalizes the animal and to me wouldn´t be that natural sentence.

   Anyway, my student faculties aren´t that sharp today, so let´s wait others contributors have their say.

    PP.