Neutering is a pretty routine thing now a days, I'm sure he'll be fine.
At 8 months, wanting to get out and run is normal for an energetic puppy.
Breeding a dog is so much more involved than "let's make beautiful puppies". Since you have a male, it would require you to look for a female, then the female owner would have to "approve" your dog..You'd also have to show OFA's of hips/elbows and any other health clearances, (if the female owner doesn't, why would anyone take the chance and breed to her? irresponsible in my book)
While I think health clearances are most important, temperament is a huge issue with me, beauty isn't everything, I want a sound solid dog who is as near perfection as it can get.
I could go on and on, about why breeding a 'nice beautiful gsd' is not the greatest thing in the world, but to suffice it to say, I tell people who would like to use my male, "go get one where he came from..because you admire him, doesn't mean he'll produce himself,,his parents on the other hand have a better shot of producing 'him' than he does"..
So you did the right thing, there is enough GSD's in rescue who need a home. There is such an abundant amount of breeders out there to choose another dog from.
OH just on a side note, keep him toned down for a week or two (I'm sure your vet will tell you this)..My male was neutered when he was almost 3, he got out on me after 4 days of rest and one maniacal run around the yard did him in,,his 'sac', grew larger than pre-neutering (YIKES) and filled with fluid, had to be drained off, which I'm told is not uncommon with males who don't keep it toned down for a few days)
good luck with your boy
diane