Don't expect to get rich off being a massage therapist, but it is an enjoyable profession for someone who likes people and feels rewarded when they see people get better as a direct result of their working with them. A therapist starting out usually finds it necessary to work in a spa/clinic environment at least until they have enough of a reputation to be able to go out on their own. You'll make more money on your own, but then you also have to cover your own overhead and advertising. There's a certain amount of safety in working in a spa/clinic too. The "horror" stories usually come from women working on their own.
What you wear depends on what kind of environment you are working in. Spas and clinics tend to have their therapist wear scrubs. If you're working on your own, casual clothes that allow you to move comfortably is fine... but you don't want to look TOO casual... need to have a professional appearance.
Another thing you should consider is the wear and tear of massage on your own body. If you are doing deep tissue and other massage techniques that involve real work on your part, there is a toll that your own body takes after awhile. My massage instructor once said that the "average" professional life expectancy of a therapist working full-time is 7 years before she starts to experiences the occupational effects like carpal tunnel, back aches, etc.