if ur goal is to grow the scene i don't think single-div tournaments will do anything for that, and honestly i dont think cups will do that much for it in general
probably the only way to grow the community through cups would be to work with a pub community or newbie mixes or something to host a newbies-only cup with experienced coaches and a small prize pool (something like 12 keys for the winning team). i think the current newbie mix format is probably more effective and more sustainable than that though
the biggest hurdles for regular community cups will be awareness and oversaturation, not prize pool or format decisions