I didn't read the entire thread, but best would be to get 1 pup at a time, get the other when the first is completly vaccinated etc.
As for agression, after vaccinating the pup you can begin its social education GSD's are great dogs and you can take them almost everywhere with you if they are socialised. And their protective streak towards their own home is also great, so you'd have a fine companion in them.
Labs are smart too, but they are not bred to be watch/ guard dogs, and need more exercise then the gsd, also have a tendancy to put on weight. But they are popular coz they r smart, no agression issues even with a minimal or no socialization effort.