i think he can use 4 or 5
it is said that avg jounin have 3 elements.
minato being promoted as hokage means he must have atleast 4.
Being jounin or Hokage doesnt matter for your elements. If you have 2 as a jounin and you get promoted to Hokage, you dont get more elements all of a sudden.
Most jounin have 2 btw (that is what kakashi said at least).
Hashirama, water and earth.
Tobirama, water and maybe more (Kisame could use earth for example).
Hiruzen, Fire and Earth are shown, maybe he had more).
Tsunade has not shown elements, but might have them. She had send electricity through Kabuto, that might imply lightning.
Minato has not shown elements, I suspect water and wind, due to Namikaze meanign waves and wind and both natures work well with Rasengan. Minato has been shown to slice things apart like Bee his tails (maybe he used a subtle wind element).
Onoki has 3. Muu has 3. Raikages only seem to use 1, I dont know if they have more.
Mizukage Mei has 3, water, earth and fire.
As you see, Kage and shinobi in general rarely have 4 let alone 5.
