Before you begin any FWB shenanigans, you need to be aware that this is not a typical (and sometimes not a particularly healthy) sort of relationship. Make sure you are ready for it. Even for those of us who are far from clingy and even prone to scandalous behavior, a FWB situation can be difficult to master. Feelings often get involved, even when you don't mean for them to.
That's why, before starting anything of the sort, you need to be upfront with yourself about your expectations and your limits. Do you really think you can do this without getting hurt? Will you be okay if and when your FWB strays or finds someone they want an actual relationship with?