There are many factors involved in choosing a particular conference, but it is important to attend and/or participate in much as possible.
It is not about the number, it is about choosing one that fits the project the most and can bring the most benefits to the project.Attending conferences is not cheap so it is better to be strategical about them.
I agree, but I think the location is mostly decisive, hardly that everyone can go to the other side world for some conference, so the project mostly attend those in region.
Nowadays teams are spread all over the world, so that should not be too big of an issue