Deefur Dog

Hi All, Am new to this an need a little help.....so for the little story but gives you a bit of back round. Me and my partner rehomed a 9 month old German Shepherd from a family near us he wasn't looked after hardly walked, wasn't socailized had a muzzle on all the time but was surround be kids. once i picked him up he took to me like a moth to fire, but not so well with my partner. of which he doesn't listen to and just ignores but he follows me every where and waits by the dog till i come in etc etc. But we are having a few problems: 1) when walking if he see's another dog hes pulling barking and goes mad until the dog has passed not agressive unless a small dog. 2) nipping and biting tried to punish him from tap on the nose to shouting to putting out side (which works at the mo) but the rest he sees as a game 3)call back is ok until he sees another dog / animal then hes gone until he wants to come back no treat works. 4)pulling on the lead treats again he doesn't seem to be interested unless in the house....of which he can do most things .....he isn't dump for sure. we take him training, do mind stimulation, tricks, games very long walks but still can be a pain. I know its our/my fault just need to know where am going wrong any help i would greatful thanks