1. I don't think it should be a problem. Cats can hold it when they need to.
2. I don't have an issue with the smell (and I keep mine in my bedroom
). I scoop once a day. I also replace all the litter and scrub the litter box down every two weeks.
4. If the kitty has diarrhea, it needs to see a vet. My cat will occasionally exit the litter box too quickly so that some poop ends up outside of the box, but it doesn't happen very often.
5. My cat doesn't have any issues with being away from me during the day. He has plenty of windows and cat toys to keep him occupied. I always spend some time before work and after work playing with him, so you might want to reserve some time for that. I'm not really sure why you'd keep your cat out of your bedroom, though.
6. There are different types of litter boxes. If you're concerned about the smell, you could try experimenting with different types. My cat uses a top-entry litter box. I know he prefers an open box, but I don't like the litter being spread everywhere.
said, cats can have urinary issues. Mine developed crystals in January. I didn't realize anything was wrong until I saw him going back and forth from the litter box for 30 minutes straight. I had to take him to the emergency vet. It turns out he doesn't like drinking water. Now he eats all wet food with added water, and even though he has a water bowl, he never touches it.
All of the other cats I've known have been fed dry food without any issues, but it's something to be aware of. I never bothered to monitor my cat's litter box until he got sick. I should have seen that he wasn't peeing that much.