AFAIK no, but would be very cool to do so.
No, and I think this could be difficult to implement compared to other things, and I guess many warlords would likely not be fond of the idea of other people messing with their clan's stuff. Depends on the person, I guess.
If I recall well there's no clan limit, but a grand total limit of 4000 players per alliance. This info is years old, however. Someone correct me if outdated.
You choose the PS account as your primary. Whatever little stuff you have on your PC account will be added to your PS/new-multiplatform account and you'll be able to access it in any platform of your choosing. Including PC.
(PSN)Hikuro-93's post in What can clan alliances do nowadays? was marked as the answer