I have a GSP!- my dog coming up for ten years old now. As with most dogs & people partnerships, everyone's generally really biased positvely on their choice, but with as much objectivity as I can offer, I think as long as you can carefully manage the early stages of accepting and teaching that the existing livestock is off-limits as prey, you shoudl be good.
The beauty of my GSP is that she is extremely trainable, really very keen to please and food motivated, so with a bit of skill and patience on our part, can train to do pretty much anything within reason. Really sound with my kid when we got her (kid was about 8) , they're still best frieinds. He stared uni in october and she still looks around the house for him now and again.
As with all puppies, the early years with bundles and bundles of energy is where you need to be on your game to channel that into something positive. I used to take Madge for ten mile + bike rides, never really managed to tire her out.
I've had a few dogs over the years, cross breeds mainly, and I'd say that my GSP Madge was /is one the easiest to train . Mind you, she is still a pain at greeting people who come in the house, she's all over them with excitement, not aggression - never really managed to sort that out. But thats on me not the dog.
TLDR is Yes GSP great but also yes, they need plenty of exercise- like all / most dogs- we do mainly 4 mile walks daily off lead, with much longer bigger at weekends and all is fine.