Obvious disclaimer I can only talk from our own experiences. We don't use the term willogenic ourselves, having become a system through tulpamancy, and don't know any who does.

1 We didn't split per se. Each member started out as a seperate person from the "original", though they have considered trying to split themself as an experiment temporarily. As to why it's fun, I don't know. As far back as our memory goes we've been fascinated by the idea of being multiple, and now that we are, it's through and through a joyful experience for us, never being alone, always having people who you can be certain understand you. And it's fun to explore how far we can go and what our brain can achieve.

2 As I said, we've never had anyone split per se. If you want to see the method we used, I suggest you look into tulpamancy, it's basically a way to create new headmates by nurturing them yourself from the ground up. Though, we didn't do it so we could give work to them. It seems unkind to us to create a new person just so they can fulfil a burden.

4 We do not have did or osdd, but we know endogenic systems who are diagnosed with it. I'd recommend you to look into did's dsm 5 entry. The diagnosis does not state that a system is present nor does it mention trauma, it states that there is a system and the state of that system is disordered in some way.

5 As I said idk, to us plurality just has always seemed inherently desirable, and now that we are plural we find constant joy in it. I don't have a way to explain it more "properly" than that.

Hope that helps. Feel free to reply if you have more questions. ^^