Feeding my Mini.. HELP!?

I'm buying a mini soon, idk whats feed its on right now. It WILL be on all gr, and goood hay, so what should I feed it? Ik some minis that are just on hay strecher and some that are on nothing and some just get what the other horses get just smaller portions. my horse gets 12% sweet feed and purina endurance, could i give it small amounts of that?