I'm pretty busy too. Just got to find a server that matches your lifestyle/playstyle with others that are in similar situations. No one is going to expect you to play 12+ hours a day. I usually am only able to log 1-2 hours on my MP server with no issues. Keep in mind that if you are wanting to advance at a similar rate as other players, this will take you logging more hours. As long as you are okay with slow progression, than MP may be the right choice for you.