I had a lot of the same fears as the OP and I'm with my first GSD and she's a working line.
I think the fact that the OP is worried about these things goes a long way into helping prevent them!
The key is to have the money saved up to do puppy classes and make sure you have a great training place lined up before you go. SOCIALIZE SOCIALIZE SOCIALIZE. It is NEVER ENDING socialization, especially with a young pup. try to do stuff iwth your pup almost every day, I'm not kidding. Training, training and then more training!
I also love checking out dog sports with my pup. She's too young to do much (6 months), but I can at least bring her along to socialize and hang out, other dog people are very understanding if she starts to bark etc., not like the looks you get if you're out around town.
You get the training and socializing right and you'll have a dog that's better than you ever thought possible.
They can make you want to pull your hair out. I swear my pup's personality changed every other week! They go through fear stages, get these funny quirks, then lose them as fast as they came. I had no idea how strong a bond we'd have right from the first day, I won't lie, I was completely overwhelmed by it.
The first few weeks were really hard. There were tears. There were worried phone calls to the breeder - just another reason to make sure you find a really great breeder. Don't underestimate how important a good breeder is. She was there for me when I needed her and let me know all the things we were going through were normal, and gave me a lot of help in how to work through problems.
I can't imagine not having her in my life. Even when I roll over at 4:00am and I hear her tail wag a few times in hopes that I'm getting up (keep dreaming!), I smile. She's my best friend, and now that the hardest part of puppyhood is behind us, I already want to get another!
GSD's are addictive! Something I never would have believed the first month I had her. lol
Do your homework on what lines you're interested in. WL are high energy and will sometimes challenge their handlers a bit more, but IMHO, they are sounder and have better nerves. I love that drive they have.
Just be prepared to work your butt off with your new pup, and it will turn out just fine.
I found this was a good explanation of some of the differences in the types of GSD's out there:
Von Öhmke - German Shepherd Dogs