I'm not likely to have such a situation in my family as a single and since I find taking care of a dog to cramp my style a bit and with a dog there's no consequences for leaving your 7 year old home alone for hours at a time. So I can't see myself adopting a kid as a single, and don't know of anyone who would be likely to leave me a kid that would change my mind.
I think you can still do errands and have alone time when the kid is at school. Doing stuff during the evenings/ weekends is not really an option unless you find a reliable sitter or friend/relative. On cramping your style, marriage, kids, pets, etc do take away aome freedom.