''his temper is not the greatest.'' This is the biggest and most vital problem you have. If he isn't neutered, muzzle him and get him to the vet to be neutered. Take a stool sample and have it checked. If he has worms, the vet can prescribe the proper, effective remedy.
If you bought him from a breeder, let the breeder know you are unhappy with his
aggression. It is absolutely wrong to breed aggressive dogs. If the dog does
not respond to discipline, you may have to destroy him. Let everyone else know
where you got the dog and the problems you are having. Breeders that breed
aggressive dogs, should be run out of business.
I am not sure my usual suggestion of better leadership will be enough in this case. You may need a professional dog trainer. He may be unfit to take to a class now. The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at
Raising Your Dog with the Monks of New Skete For more on being top dog, see
Establishing and Keeping Alpha Position, Letting your dog know you are the boss
As for the weight, it is quite normal for a young Shepherd to be on the thin side, and even having the ribs show a little.