I was single with a large dog in an apartment/condo setting for 8 years of my life. As long as you are willing to commit to what the dog needs, then there is nothing wrong with it (even a large dog in a small space is fine, depending on the breed). It certainly sounds like you know what to expect, so I would tell the nay-sayers to mind their own business!

I'm sure you already know this, but definitely pay attention to breed (as best you can with a shelter dog). You don't want a jack russell or border collie mix unless it's a much older dog. These are breed types that are high energy, working type dogs and they'll go nuts inside all day. On the other hand, many BIG dogs are very content being quiet all day (like Great Danes - if you wanna really freak out your neighbors!). My dog was a shephard/dobie mix and she had no trouble with 10 hours alone (figure in commute, too) as long as she got plenty of attention and exercise when I was around. I had no life outside of work back then, so it was really, really easy to devote a lot of time to her. In fact, I find that I very much miss that one on one connection that we had. She'll forever be the best dog I ever had and I miss her terribly, still.

Please share pics when you find your next companion!