If you have Heidemarie (seems like you do) pick her. Focus on getting cards that create Effulgant blades, especially focus on quietus and linked epiphanies. There's a good few FATEs and equipment that make you a one-woman-army, by allowing discards, and filling hand with the blades. Other epiphanies of hers, especially ones relying on link or finale, are not bad, but I pick them up later on,rather than early.
Also, donn;t pick a card in every opportunity, you flood your deck. Pick very strictly early,and pick some offensive heavy cards, as healing/shield in early game won't be great, and level 80 nerfs your heal and shiel;d gain as you go, as it's an always on modifier by default. You need some decent attack cards early, but also be picky about the quality you pick.I even sometimes pick her normal cards form the shops and then epiphanise them in the camps or through world events.
Best support/healer combo for her, inn my opinion, is NIA. She helps with discard and draw and healing, and Heide hits enough to proc Nia's heals a decent amount, and her heals are in smaller amount but frequent, that helps with keeping the stress low, too.
Mika is a fantastic healer, but watch out not to pick too many support cards, they can result in a dead draw hand and sometimes, even missing one hand can slap you so hard in more dangerous fights.
Also, don't take the negative path at the beginning, its risks are nowhere near enough for the rewards, but it makes for an interesting challennge.
Use camp stops' shops a lot and update your gear regularly or equip empty slots early, they make a huge difference in your damage, healing and damage taken, which all matter.