Rule of thumb - if you see your fwb more often than once a week, she will turn like a Cinderella into a pumpkin. No more than once a week. Words and explanations of how you should only have sex and nothing exclusive wont help, even if she agrees. More than once a week will lead to bonding. Also make sure she knows you have other girlfriends (even if you dont).
And yes you can take her out, if you want to (i wouldnt call it a date though, since it has a girlfriend-boyfriend frame), the only rule is no more than once a week on average.
Being a friend in FWB has different degrees. I have an FWB for several years now, who is my good friend, and there was a time when she had a boyfriend, we didnt have sex but still would have a coffee every once in a while. After her BF was gone we had our usual sex routine again.
FWB relationships require more commitment from a girl than exclusive relationships, thus you need to build it from the very beginning, from the first time you meet a girl, but remember sooner or later, one way or another the girl will be making attempts to convert you into exclusive.