We have had 5 white GSDs and a Huskyx (RSPCA thought she was a GSD, but she wasn't). Please ignore the suggestions for getting a Husky without LOADS and LOADS of research (start with ToBoldlyGo as she's ace)
We didn''t choose to have whites, they kinda chose us except one which we bought from a supposedly reputable breeder, who had the worst hip dysplasia our Vet had seen. The rest of our dogs are rescue and I will only ever have rescues from now on.
We currently have 2 still with us. They both bark A Lot. One male, one female. I think in temperament, I favour males as they seem less work. Both are aggressive but this is not the breed's fault, the other 3 weren't agrressive. Of the 2 we have, one was kept in a too small upstairs flat (she has HD), too little socialisation, too little training and has an aversion to anything long (i.e. baseball bat shape) and Feet. The other was kept in a dark room, with no socialisation until the breeder gave up trying to sell him and his brothers and dumped them in a rescue at 10 months.
I second all the health and breeding comments above. Treated right, they have amazing temperaments. Get one from a rescue, preferably who uses fosterers. I've chosen to have the ones that were given up by numpties who got them for looks/guarding and then didn't put in the time to train them.
Tons of exercise and mental stimulation.
They have a tendency to bond strongly with one member of the family - this must be discouraged as they can then turn on other members of the family to "protect" their particular favourite. They need clear rules but respond perfectly to treat training - they love to please you, unlike my Husky who believes we live to please her 
They do suffer with seperation anxiety so it's good you have someone around most of the time. With your DS and cat, there is nothing in the breed that says you shouldn't have a GSD, but again, if you get one from a reputable rescue, they will have cat tested them, and if it has come from a fosterer, they can tell you what he is like with kids. But, they are powerful dogs, so never leave dog and child unsupervised. You will also need to teach your son to respect the dog etc.
Hope that essay helped
. If you go down this route, please feel free to ask me for advice - having had 5, by now I must have hit most problems with them
but having said that, they still seem to teach me something new each day.