I currently play in s.1840 and here is my personal plan for 20k milestone. (We are given Kushina 3* last week, and 20k milestone has 48 jiraiya fragments note these, February is bringing a selection pack with 80 frags of Izuna, Kushina, Shisui, Dan Kato in it)

-Buy 32 Jiraiya frags from Banner (11,2k)

-Get 20 Kushina fragments from Sage Key by rolling weekly free keys. (2,5-3k, let's say 3)

-Current Sum is 14,2k

-Use the remaining 5,8 on wheel for some power materials (Train pots. Or keys to at least 1050 the rebate)

-Collect Feb packs, enjoy your 4* Kushina and Jiraiya Toad Chant team.