What I have learned since is that Demon Mode is incredibly unforgiving when it comes to HP, Delaying Enemy attacks and especially reducing them even if just temporarily saved my life more often than not. I ended up going with a horde build that I wouldn't recommend but overall having a gameplan early really helps.
I ended up spending a lot of my early game focusing on big combos in my opening to rush through the weaker early enemies, getting utility sigils that made it easier to build into strong builds and especially having a defensive sigil early will help you in the long run.
Generally taking risky plays against elite enemies pays off better than trying to play it safe as well but always keep you HP in mind as there are some enemies like the Sentinal that can hit like a brick house while also being build like one. If you're underprepared for any an enemy who's tactic is to just stall our the fight, consider safe plays that preserve your HP.
Regardless, I'm done now, good luck to all y'all
Edit:
Nearly forgot about this but keep in mind the order in which your sigils are lined up as the effects always take place from top to bottom. So if you have any percentile increases to your damage, be sure to have them low on the lineup to maximize your damage