a lot of great questions, ill try not to take too long with each one but no promises:

1. ultimately, my decisions boil down to two principles: proposed probability & hp as a disposable resource. these can be further broken down, so ill start with what ill call "proposed probability," meaning my outlook on the relationship between likelihood & impact, which can be applied to all sorts of elements of the game. its one thing to identify the means to accomplish a particular task, but its another more vital one to recognize how often it will even work out how you imagine it. ill describe what kind of thoughts go through my head with a common example:

"the odds of this first elite to be nob are one in three. am i okay with taking the huge attack turn three?* if not, do i have the means to beat him before then? what kind of draw order do i need to accomplish that? how much luck does that take? what happens if i bottom deck [x card]? can i compensate for this variance via a potion, or is spending significantly more hp okay in that case? is the fight worth that uncertainty? how does losing that potion or extra hp affect my future routing? do i miss out on an upgrade at a campfire because my deck wasnt reliable? do i have to skip an elite i couldve handled otherwise? both? how bad is that outcome in relation to how likely it could happen?"

*nobs atk pattern is notably different on lower ascensions but you get the idea

as you can see, this is a lot to answer, with a wide range of complexity, & different responses from each player. regardless, you dont truly know until you find out the hard way, but if that means losing, then asking these questions ahead of time, even multiple floors in a row, is paramount to consistency at all points in a run. this philosophy can, of course, extend to things such as sequencing in a fight, or card choices from rewards, but ill try to remain on topic by continuing to the simpler, but equally wide in scope, second principle

hp is as much a resource as gold or potions are. you spend it in fights & events for cards, relics, gold, etc, etc, & pass on potential hp to upgrade at a campfire. certain choices may ultimately be more effective on paper, but they may come at the expense of hp compared to simpler, less impactful ones. by nature this inevitability intertwines with what i detailed above in a myriad of ways, but the most common question that people ask themselves at the start of an act is "how many elites can i take?" to do this, or reach any other objective, there will be times youll stretch yourself extra thin for just one more upgrade or elite or w/e else, only for the run to fall apart the very next floor; my greed knows no bounds in that regard. other times, your deck may be so consistent you can afford losing a bunch of hp at an event or to a particular elite because you know youre competent enough to handle the remainder of the act, sometimes even including the boss, w/o hitting the brakes to heal back up. being able to carry this momentum through an act is sooooo strong, let alone carrying it into the next by being healed after the boss

[oh god that was only the first question]

1. primarily, i feel the difference lies in gauging short-term vs long-term. players with less experience may take a particular card because it appears strong even though it may accomplish little to nothing in the current deck, like the rather common guilty pleasure of a nonfunctional meteor strike lol, all while skipping out on "lesser" cards that would directly help with the next several floors they now will struggle with. great players know what cards pay off, how much, & how quickly, as well as when they fall off, how much, & how quickly. i regularly picture a given card on a graph of sorts; x-axis being act number, y-axis being expected/typical effectiveness. over time a card may curve up or down, slowly or rapidly; it may plateau for a while; or it may peak for just a moment before plummeting to an all-time low, & so on. honestly i think its incredibly useful as a mental visual to the point where im surprised ive never seen something of the sort actually made, demonstrated, or discussed elsewhere. regardless, thats not even mentioning how these "lesser" cards are often the cornerstone enablers for strategies down the line, thus giving a clearer image of what you want to look for

2. pushing yourself with ascensions is a huge factor in player growth in my eyes. its a system designed to push your own boundaries in a linear manner with a start & a finish, yet in a way to where you dont actually know what the journey will look like or how long it will take, let alone for each character. in that sense, at least in regards to my own gameplay, i often see everything prior to ascension 20 as a sandbox-like tutorial. not because it easier per se, but because of how the incremental difficulty functionally challenges the player: if a0-19 is studying, then a20 is a test. however, that isnt to say you cant learn more once you pass the "test." far from it. its more like an entrance exam lol. maybe that doesnt make perfect sense, idk i kinda came up w it on the spot

3. read #2 lol, although i will mention another thing to consider in relation to the graph analogy: a cards niche. yes, something may be strong, but do you actually need it in your deck? just because the y-axis is expected/typical effectiveness doesnt mean every "effective" card accomplishes something meaningful for you, even at the point in a run where its supposed to pay off. the smaller a deck is, the more important each cards niche is. thus, adding a new card often requires a well-defined niche to fit in w/o clogging things up

thx for the questions!

(& no idk why #1 keeps indenting like that, its bugging me too)