If you don't feel ready emotionally, don't do it.
That, it seems to me, is a very basic guideline to follow when considering entering any serious relationship. If you're not emotionally ready for the dance of relationship and all that can happen, then stay away. One can be uncertain as to how well it work out and how long it might last. I don't think one can be uncertain as to whether one is ready or not and still ethically get involved.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.