It works out just fine...there are days when you don't really want to go out for a walk...but you have a yard so you should be fine. The dog doesn't need a lot of room inside as long as you exercise it plenty outside.
The hardest part is probably when you decide to move...if you're going to another apartment you might have issues finding one that allows GSDs.
That's my opinion too. You do have to be really committed to making sure your dog gets enough exercise/stimulation, but that's true in any situation--it's just a little more high-stakes if you're renting since a bored dog can be very destructive and/or noisy, which landlords tend to frown on.
If you feed your dog a high-quality food and groom them appropriately, there really shouldn't be too much of a smell. I'm actually pretty sure I haven't bathed my GSD since August or September just because I haven't needed to--his skin and coat are healthy and he doesn't smell unless you actually put your nose on him and sniff, and even then it's a nice smell.
I brush him 2-3 times a week and feed him very good-quality food though. When I didn't know any better and fed my dogs cheap food, they smelled a lot worse and needed frequent bathing.
If you get a puppy or a dog who isn't house-trained you'll have to expect them to have some accidents as they learn, but prompt cleaning and an enzymatic cleaner combined with good training and management (so they learn quickly and don't have many opportunities to go inside) should make that easy to fix.
Are you planning on spaying your female? If not, you'll have to be prepared for some mess when she's in heat, and a lot of landlords don't allow intact dogs. Also, you mention you'd only move into your grandparents' house, but are you planning for the entire life of the dog? Keep in mind that a GSD can live to be 10-14 years old.
Overall, it's very doable but keeping a high-energy dog in general is a lot of work, and keeping one in a small rented space is a little more work on top of that.