Thanks for the feedback, and for reading through my big wall of text! Yeah, this is all pretty theoretical for me too. Playtesting will reveal the truth, haha.
Regarding wounds, yeah, it might end up not feeling very fun to have your deck clogged up. It works pretty well in Mage Knight (Slay the Spire still has HP, but it has other status effects as cards). Removing player health is part of the design I'm most uncertain of... I could potentially still do status effects as cards and change enemies to have 1hp, but still keep multiple hp for the player. We'll see how it works.
Currently there's no indication of enemies current health. Armor and other status effects are mentioned in the action log, but I don't expect anyone to closely read that in general. Less things to track for the player is definitely one of my motivations for single hp. I'm not too worried about removing cards... The cards in the game right now are basically the only ones I could think of during the first few days, but I've had lots of other ideas during and after the 7DRL.
That transitions into your final point about card balance. I definitely agree with you there. Flash, Open Your Mind, and some others end being pretty obvious choices most of the time. And then others are I almost never choose, though I just buffed a couple of those. It's definitely an ongoing effort. I definitely don't want any card to be automatic grab or automatic skip. I want to focus on those bigger changes above first though, since they will have a big impact on the cards.
One tangentially related change I'm considering is adding variations on the levels, that are weighted towards different enemy/card types, to give the player a bit more choice about how to build their decks. For example, you could choose between going to a level with mostly slime enemies, or a level with a mix of mushroom and crystal, etc. with not all combinations always available. That might help each run feel a bit a different and make the deck building more interesting.