I'm not sure what all you know, so I'm going to tell you things that are blatant obvious. Not to insult your intelligence but posts like these circulate a long time, I find myself reading threads from 2011 rather often, so it's also for them.
I seriously commend you for such a large time gap to really allow yourself to know the breed, it's lines, and build yourself up. Now, with that said, get your first GSD of GOOD QUALITY. I emphasize good quality because my GSD was an ASL and he would have completely turned me off if I hadn't researched more and realized I was expecting a WL out of a SL.. Don't expect to breed your first dog, you will most likely mess up and need to learn your training style and such that your first "serious" dog will teach you. From there start to title it. I'm to understand you want breed service dogs? I don't understand much about that field but start with titling in obedience. It only makes sense that a great service dog has a phenomenal foundation in obedience. Also, get started in figuring out which type of GSD you want to start it. I don't think a puppy with a long lineage of police K9's would be the /best/ fit. However, a puppy with a long lineage of versatility would be a much better option, and you may decide that a hard, drivey WL isn't in your breeding imagine, but a ASL/WGSL is, which are regarded as softer and less "demanding."
Do as much research as you can, good luck! I hope you keep us updated in your adventure!
Sent from my SM-G900T using Tapatalk