Heroine will eventually forced to wear if you won't pay the rent.
But outfits are another wasted opportunity in this game because after 1/3 of the game heroine is just naked in every scene...
Using spell book is a strategy

Personally, I used whatever weapon I found first. I also wanted to explore (until I found out that it's pointless and inefficient...) every room so things got tricky at times since all monsters just converge on you.
I didn't play on the hardest difficulty but one below it and I can see that there's some depth in this game (movement, equipment, skills, crown control, etc.). But there's too many annoyances and too little payoff (tbh, there's no payoff at all after completing dungeon after the first time). There are no bosses at the end of dungeons so all your progression and powering up is pointless - your goal is to rush to the stairs...
I never play these things on hard, just go for 'normal' all the time. Hard generally just means more meaningless farming/grinding, which is generally boring as H***.
Unlike a game like DMC where hard actually gets manageable by gaining some skill in the game, these games ... yeah, not so much.
I never go for easy either though. Must be the leftovers of a gamer's pride I guess. Even though many games that offer it ain't really worth it for the gameplay anyway.
The base game generally ain't the main draw of an eroge in the first place ya know (most of them anyway). This game ain't no different TBH.
Other than that, I've barely had any floors so far that I haven't fully explored. I AM an RPG fan and the OCD of a map completion just sticks with ya.

Even with the turn limitation they push onto you starting dungeon 3.
Even so, sure I've only completed up to the 3rd dungeon so far, but just going all willy nilly has worked out just fine.
As for the book being strategy ... starting from the 3rd dungeon you kind of HAVE TO go with the first weapon you find, as you enter ... with literally nothing.
And my frustration I typed out earlier of course where after finishing that level you're forced to take out all your 'current' equipment.
Anyway ... as soon as I found a spell book, I switched to that for the extended range benefit. Of course that took quite a few floors to once again get one after starting from scratch again, but still.
And yeah ... I suppose that'll be the same for the 4th dungeon, in which yet another succubus is housed, in which I once again won't be able to bring anything in, meaning you're again forced to start over. Even if it turns out the 'same' item storage box 'transfers over', it's still F'd since all my current equipment was forced out! Basically making all the 'depth' useless and just plain annoying, not to mention abhorrently frustrating.
I haven't risked 'building' a piece of gear so far with element upgrades, but imagine spending all that effort into building a perfect piece of gear, with perfectly chosen/farmed elements ... only to be forced to render it obsolete and literally unusable right after!
Even a damn proper roguelike game, which starts you over at the beginning each time you die (games like Returnal for example) has the basic decency to build up your arsenal/toolkit (and usually shortcuts) to allow you to get to where you died last in a faster fashion (than the first time you did it).
Haven't played Returnal yet, but that's kind of the basic premise of the style of game that keeps returning you to the beginning ain't it.