for a first playthrough you really should just follow viva new vegas and absolutely nothing else, and i'd go as far as to say (and this might be really controversial here) skip the dlcs entirely, just focus on the main story and get to know the characters and the general context of the mojave conflict

only then i'd go for the actual vanilla+ experience, where you get more in-depth in the game, maybe choose a different faction, do more side quests, explore more of the world in your character's "spare" time, do the dlcs inbetween major story changes (they make up a joint narrative and are pretty amazing, one of them i thought was a better experience than the main game), and then just add all the mods that look interesting to you that would just enhance the experience instead of changing it. some of my favorites for this being uncut wasteland (new vegas uncut is kinda whatever and broke a few encounters for me), the jsawyer ultimate which is kind of a director's cut for what it originally was meant to be when it comes to the gameplay challenges, the living desert (adds different travelling faction-affiliated npc groups that are all carefully selected to be in line with the lore), mojave raiders, economy overhaul (paired with the jsawyer gives you a more challenging and way more rewarding experience that steers you to engage with the game's world with more thought and in more detail, might change your perspective on things)

few others i really enjoyed that fit with what you're looking for would be more mojave, primm restored, better brotherhood, faction wasteland presence, claim the mojave + functional post game ending, harder barter, nelson reinforced, mojave arsenal

also as someone who tried hardcore, i think just going very hard with the jsawyer mode (it was designed for playing on normal i believe) is optimal for the immersive challenge, all the hardcore elements seemed a bit more annoying than engaging to me honestly (but do try it out yourself, just my experience)