Most Helpful Guy
Before would be best. One of the main benefits if you met them online is you can discuss all kinds of stuff before actually meeting in person. I think in person it would be much more awkward to talk about stuff like that until you have been together a while, and by then, you may be too concerned with what they will think of you and if it will affect your relationship negatively to let them know what you like.
Most Helpful Girl
If you need your kinks catered to then you need to make sure that person is willing to work on it with you otherwise there’s no point in getting involved