You don't need many techniques to become Hokage, nor do you need to be the most powerful ninja in the village. All you need to do is love the people you'll be watching over, and love the village. Sarutobi would pass on the title of Hokage to Minato not because of his incredible speed or his techniques, but because of his faith in that which he shall be succeeding, and the duties it holds.
You must be registered for see images
You must be registered for see images
It's not about power. It's about raising up a generation of ninja, and having faith in them to lead on, just as the Hokage now was left with the same fire from the previous. "That's what it means to be Hokage!"
Yes, I agree. You need love for the people. You need passion of konoha. But that doesn't mean squat if you're weak. You need to be strong and powerfull in order to protect the people. Every single Hokage has been the strongest Ninja in Konoha at their time. They have to be. And every Kage is the same.
I assume that Madara is capable of a lot more than what he has shown so far. And the same goes for Minato. He has to be stronger than what we saw. He should have at least mastered one element, and be proficient in all areas of jutsu (genjutsu, taijutsu, ninjutsu). It's common sense.
Examples:
1st- Mastered ninjutsus (water, earth and wood), taijutsu, sealing techniques and was proficient with genjutsu
2nd- Mastered ninjutsus (water, apparently space and time), taijutsu and was knoledgeble of genjutsu and sealing techs.
3rd- Mastered ninjutsu (suppose to know every jutsu in konoha(even if he can't perform them) and we have at least seen him used high levels of fire and earth tecniques), taijutsu, sealing jutsu and was knowledgable of genjutsu.
5th- Mastered ninjutsu (high level of healing techs and basic jutsus), taijutsu, sealing jutsu and had knowledge of genjutsu.
Soooooo, one can assume that minato mastered at least:
Ninjutsu- at least one element + his space time tech
Taijutsu- all kages so far have been strong with it, so he has to be also
Sealing- He used high levels of seals (death god, eight tigrams, contract) and his space time jutsu is also based on a high level sealing tech
And he has to be at least knowledgeble of genjutsu.
He just happens to have used the areas that granted him the most effective defense against Madara, but he didn't use all of his techniques.
Oh and to use kage bushin when he fought Madara would be a mistake. He would split his chakra in two and except for Naruto, spliting your chakra in two gives you a great handicap. No other character in the series can use kage bushin effectivly except for naruto itachi and kakashi. For all others it's hard and useless. In this case, Madara would have beaten a clone easily. Besides, we don't even know if the flying thunder god technique is compatible with kage bushin. Remember that there are some techniques that the clones can't perform, like genjutsu for example.
I just think that if one assumes that Madara has more up his sleeve, it's only logical to assume that Minato had as well.