How to farm/get a build going in WotN?

After finishing Nioh 3 I decided to check out Nioh 2 again where I left off, but I cannot manage to progress more than a few floors of the Underworld. I'm around level 450, with random pieces of 190+40 Ethereal gear that don't really synergize. Any suggestions on farming spots, and/or builds I can play to get it going? Are there any "must haves" in terms of sets, affixes, onmyo etc?