I don't see it as any different to a vanilla relationship save that you tend to be more circumspect about what you want. In answer to the question - yes to all of them. I think online is one way because you can be more open about what you want.

A good way to find someone is to get involved in the local scene - go to a munch and meet people there. At the very least you start off the whole 'dating process' with the knowledge that you are meeting people who are already involved in the scene and therefore already a sub/switch/Dom.

I have also learnt that those in the alternative scenes (rock/goth/metal etc) are more likely to be at least interested in BDSM in a perpheral way if not already involved so again the chances increase of meeting someone who is interested.

However, overall there is a lack of good dom/mes and an excess of subs of both genders so the competition is tight...