I was able to pull off raising a puppy while working full time only because I had a lot of options when it came to taking puppy out to potty all the time and feeding him in the afternoon.
My room mates here all work at different hours, so during the baby stages of his life my pup was taken out every hour on the hour even if I wasn't home. How lucky is that? He is turning out fine though and no longer needs help during the day. He goes a full day now without any potty breaks when I am out at work. Good boy!
You're situation sounds like it would really be tough to raise a puppy, only because of the potty issue. If you really wanted a puppy, I don't think it would be impossible. You could train him to use potty pads and keep him in a pen in the kitchen or something with his crate in there and everything. People have done it before. You just would have some extra work to do once he gained more bladder/bowel control in teaching him to start holding everything inside and weaning him off the potty pads.
All in all, I think you may have the right idea in rescuing an adult rottie
It would be a lot easier, and hey you won't have to go through the nippy annoying stage either lol!