just know these things:

1) there are events where is sure to piece jonin minato fragments 1 by 1, so if you invest on him you are sure to recruit him

2) during the past 12 months hokage minato appeared only as the top prize in wheels like this one. This means is not sure at all that you'll be able to get him. That said could be you are lucky and you get him out of 10 rolls or that you are unlucky and you don't get him out of wasting 30k+ ingots.

3) naruto sage mode in china is in shops (i wonder when we will get him there...), and is 90%+ sure that you get him out of free draws in sage treasure within 1 year of free pulls.

you are welcome