I don't think anything is more common than something else in poly. There is a large variety of "ways" of doing poly from dating lifestyle to being entrenched in poly identity and it being the only way to have a relationship. Many people are single and dating poly that come here. It just so happens, I think, that couples opening their relationship have more struggle due to the fact that they are two working together. They don't have to work on things with an already established partner.
I don't think starting out poly is different for someone that is single compared to someone that isn't in terms of finding potential partners. Its when you are in it that is different. I think you will find that if you read around here you will find that any of the information discussed is valuable to anyone in relationships.
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