One of the questions popping up is on how do you decide who to write to for LetterMo/InCoWriMo if you do not have ongoing correspondence/friendship.... I joke that I put the names in an imaginary hat and pull one out! What I actually do, is read a few profiles of those participating, and decide on that (whether they say a lot or not), who to write to. Maybe I have been to their hometown or nearby, or we share other hobbies and interests. However, too much commonality I think sometimes does not lead to a successful correspondence (repel - magnets?).
So far, I have received one surprise this month (still early days), but have sent 4 letters to new people.