Asking for a few advanced NIN Tips

Hello!

Though I'm now a Healer main, I've been playing NIN for a few years now. I'm hardly the best out there but I like to believe I have at least an idea of what I'm doing. As I level the class up, some questions have been popping, and I'd love to have some tips to help me re-learn a few things that I've been asking myself about. I'm not level 90 yet, so any thought is welcome. Here's what I've been wondering about:

- My Huton+Hide reset for my Mudras: Is that still doing anywhere else other than boss pulling? I've been doing it before trash pull as well out of habit, but I'm starting to believe it's best to just to use Huraijin on whatever and go with that?

- I once heard that if you can't get all ticks of Doton on an enemy/stack of enemies, it's better to just Katon for AoE. Was this ever right to begin with? If so, does it still apply? I remember someone also saying that it is debatable, so there may be split thoughts here?

- From what I've been testing, using the new Bunshin+Kamaitachi works well for the first trash pull, since then Bunshin is ready for the boss pull. For the boss fight though, I've been struggling to find a place for Kamaitachi in my opener, and because it stays there for a while, I've just been awkwardly placing it at the very end of the whole thing. Is there a preferred timing for it during the opener?

- I'm not sure what to make of the Raiju skills, as I've not unlocked them. From what I understand, I get access to them at level 90 upon executing Raiton. How does this interact with Hyosho Ranryu? Should I be using the Kassatsu charge on Raiton? Or keep using it for frozen Shuriken while using the other Raiton moves after a regular Raiton?

- I barely ever use Fuma... that bad?

- Anything else is welcomed!

Thanks everyone!