With Sean-nós I let the idea sift and settle for a very long time before I started putting together. Wish I'd known this was here! So, one thing I did was to minimize topic overlap w/ other similar groups. With another group I co-lead (Creideamh) I was not able to focus and go deep on Druidism w/o obscuring the other directions that group was going. So, with that and really taking input from new members and getting ppl involved fully in topic direction and such, it has really great people on board already. See link on my previous post.