He is beautiful! He looks very much like my dog
That is great you were abe to rescue him.
In addition to reading the supplied link , I would stress that given his age and given the short amount of time you have had him , you need to keep him on lead when you go anywhere. It is great that he is good with other dogs ( even though mounting is NOT really "good with other dogs" ) ..but he may really frighten someone which they do not deserve , and/or he may bound up to a dog that is very dog aggressive.
In a nutshell , it is not good dog owner etiquette to allow a dog off lead unless he is 100% in your control. My dog has been "pretty good" off lead since he was 5 or 6 months old , and now at 9 months old he is what I would "solid" off lead - but I still keep him on lead in public due to the fact that at 9 months old, though he has not shown it , he can still possibly be unpredictable ( just like kids - they may know the rules but are not mature enough to occasionally get selective hearing and break the rules when the reward is high enough - like seeing another dog ) .
Do you have a fenced area where you can do training ? Do everything on lead first , and when you feel like testing recall and such do it in a fenced in area if possible , or get one of those extremely long training leads.
Also , 5 months old is a bit young to be showing apprehension of strangers ..and you say it is particularly men and may have been in an abusive home. With all that , and considering the rather young age he is to be apprehensive of strangers approaching , I would say definitely focus on socializing him now , on lead , in allowed places. He needs to have positive encounters with trusted male friends of yours he has never met. Ask friends to help both with people socializing ad dog greeting manners!
If available in your area , an intro to obedience puppy class is a great way to socialize him , learn manners , and make friends.
Good luck , again he is beautiful. Love the name , I had a GSD i my life as a child and his name was Odin too. He was one of the great ones