From personal experience, I'd say probably no more than three - after that the subconscious mind sort of sits up in disgust and says "Hey, enough already!" Less is sometimes more.
If you have a working life then three is probably the most. If you happen to be on holidays you might manage five. More than that is just going to backfire. You are coming in with a sense of panic or impatience trying to rush it and it simply doesn't work.
If you have a lot of goals pick one and really focus on that one. The other things have a knack of falling into line to help make that one thing happen.
