He wanted to get Minato out of the way long enough for the Fox to conclude its rampage, as, according to Minato, Madara would only be able to keep him summoned for a short time.
Interesting chapter indeed, it was pretty cool to see Minato actually DO something.
There's a pretty obvious reason why Minato would never use sage mode: It simply isn't compatible with his fighting style at all. Remember, the whole trick to achieving sage mode is to stay still and concentrate on the flow of natural energy for a duration of time. Sounds like a huge detriment to a ninja whose talent lies in teleporting all over the place, no?