This question comes up a lot with interacting with other business owners on various forums. Some say its a good idea, others don't think its a good idea.
I find it hard to Focus so I don't think its a good idea for myself to focus on more than one business. I did one time try to do but I just don't think its possible unless you are already successful in your current business. I am Focusing on my Travel Biz, my Travel Booking site and I really want to do my Jerky Business. . That is still a lot to focus and only two are related.
So just be sure to do your Research and decide whether or not you can handle more than one Project.