Weather or not to take lessons is really dependent on your style of learning. Some people do great just going off on their own, and some people do better with a little direction. Look back at your previous learning experiences, how did you get by, did you listen in class or study at home? Even if you are the learn by yourself type, if you get stuck try lessons, or vice a versa. I know my teacher has helped me a ton, even though in most things I learn on my own.
There are a few things I would suggest strongly however, first learn the type of music you are most interested in, then branch out. So many people buy the wrong gear and get the wrong instructor only to stop playing in 6 weeks because they wanted to learn AC/DC not Bach, in general most people pick up an instrument to learn to play music, not that instrument. you'll want to learn to play the instrument later as your musical vocab broadens.
Also take at least a months worth of lessons just to make sure your doing it right, holding the instrument incorrectly can do serious damage to your hands and can limit your playing ability significantly.
Learn some music theory, if you've got the cash and time take the first two semesters of music theory at your local community college (watch out for classes call aural comprehension, they are a bitch, think calculus 2 for music majors). Music theory is more like science than an arbitrary set of rules, it describes how things sound, and how to analyze music. knowledge will only set you free.
in the end, nothing is forbidden everything is permissible.