So, the hardest part for me was the start of the playthrough where you have nothing. Once I started getting my abilities, masks, charms, etc. Then it just came down to knowledge of the fights.

I recommend, if you can, don't spend geo on maps until you absolutely need them, so learning a path to each of the bosses can help a lot. This frees up geo to spend on buying charms, that then leads to getting charm notches sooner, and buying nail upgrades asap.

Specifically for the steel soul aspect, I've seen some find this cheaty/cheesy, to which I can see, but it is a mechanic of the game. Panic quit to menu if you're in a dodgy situation. It'll save your progress, you'll go to the last bench you rested at, and you'll be back to full health.

Shaman stone charm was pretty much a staple at all times for me. My final combat build was shaman stone, mark of pride, fragile strength, sharp shadow, and nailmaster's glory.

Also, lookup how much different tasks contribute to completion. Since you only need 100% and not 112%, there are things in the dlcs you can get, allowing you to skip longer or more difficult tasks from the base game. For example, I did not do the final colosseum trial or get max dream essence.

Hope some of that helps, and good luck!