Check the PTS for what subject areas are on the initial CFI. Whether you get it as an Instrument or Airplane Single Engine, you are still responsible for the bulk of FOI and teaching stuff on the first CFI rating you get. CFII and MEI are misnomers. You get a Flight Instructor certificate, then you add the Instrument, Single, and Multi Airplane ratings to it based on the tasks required for that rating. Just like you get a Commercial Pilot certifiate with an Airplane Multi Engine Land rating.