What level and power are you. How much power in average are you facing in Sage? What summons do you have? What mains did you unlock if you're lower level? What ninjas do you have?

We need much much more infos.

But I try to help you out. Minato right now is super cheap. You can make a pretty good f2p team with him really early. You can get his bond skill with time aswell. You need Kid Kakashi and Kid Obito tho. Scrolls and Bells are easy to come by in the sun/moon shop. Kushina is really good yeah but in no way a carry for you. Also she got skillbroken in CN so you can't really compare her to ours.

Minato + Shikaku have great synergy, both chase each other 2 times and you get chakra + immobile.

Fire Mains new immobile removes buffs, so you c*e that round 1 against any immunes.(do it after they attack tho so it stays in round 2.)

As for your 4th depends on what you want really. You could use Gaara for the barrier, kurenai for heal + chaos, alot of options. But these 3 already offer a really good base and a good combo without any summons.