it will be OP for him to get two nature as his chakra is already OP from Sage and the Ninetails.
but itll be great if he have lightning...
two of his toads can do water and fire so itll be really super OP
this
and to add what i think about daimyo`s, they are responsible to non-ninja population which in number greater than the shinobis. And with that in mind they could not be easily overthrown.
so a daimyo`s decision is rested on how will the general population will be affected,both ninja and...
i agree with most of the above explanations, that is also why i think orochimaru despite his hands sealed, can do a number of techniques.
and for 3, i think its not only nature manipulation but also it have something to do with what clan you belong.
IMO, Kabuto and Zetsu, hell they can amass a huge number of army with different skills and stuffs. with only em that tobi guy is nothing.
now if only they can hide better.
now for the OP id say oro/kabuto. ninjas-gotta summon em all.