Buy the Sumo and MLB it first. The bonus damage will help you farm. The best farming nodes will come out after the story is done so you still have plenty of time to save up to buy Kintoki copies.
If anyone is having trouble against Ushi Gozen, try using Nobu. She has a lot of bonus damage...
I've got Chloe with MLB Sumo and Tama and Merlin with MLB Hot Springs on my list. Let me know if you guys want anything else.
For those who are new, you really want all the copies and mats for Rider Kintoki. He will carry your team on his motorcycle. Eat a bunch of apples if you need to.