5 kages.
A-on the offensive,with taijutsu,distraction
Mei- Wide Range attacks to cover A
Gaara- To stop Naruto from preparing a Bijuudama
Onoki-Flight and dust release from behind will prove tricky to stop.
Tsunade-Healer and backup offense for A.
Overall 5 kages win mid-difficulty because of teamwork.
5 Kages with high difficulty, IMO. Hard to accurately guess though seeing as we obviously haven't seen everything the Kages or Bijuu mode Naruto can do.