I'd like to get a dog but I need advice

I'm desperate for man's best friend. In fact, I think I'm slightly obsessed because I'm always stopping strangers on the street to talk to their dogs, everywhere I go! But then again, I want to be a responsible dog-owner, so I'm still thinking it through.

Any dog-owners who have some top tips on how to juggle work commitments with dog ownership? I'd have to leave the dog for about four hours a day. Is that too long? I'm told very intelligent breeds, such as collies, really hate being home alone. Are there any breeds which are more chilled out about being left? I'd be grateful for any input because it will greatly inform my decision.