I think 1 miniboss isnt good enough. I know we're not far in the RP. But you should make a kind of Application for the players too, so they can make bosses..
Too easy 0-19Easy 20-39OK 40-59Medium 60-79Strong 80-99Too Strong 100+When people send a application. You can use that ^.. As a scale for like.. Good/bad...
This would give the players something to do.