Welcome! Never too late to join the party.
The Yukari fight in Chapter 1 really is a quite an awakening to reality if you haven't got used to the mechanics. When I first got into that battle, I was lucky to have Lily White part of my team, so I could make use of the Wood breaks our beloved Herald of Spring provides and Yukari's elemental weakness to Wood. However, it is indeed quite a good point where to start learning some of the mechanics and all you have mentioned.
I've heard a lot of people saying that that difference from Normal to Hard and then Lunatic feels quite great. However, this is how I remember the things about each difficulty besides the increase in HP and barriers to break:
Normal: enemies do not use any of their abilities
Hard: enemies use their defensive abilities
Lunatic: enemies use their defensive, offensive and debuff abilities
Indeed, besides a relatively low number of character outfits, casual "oh, do you remember when...[insert reference to mainline game]" and the whole Fantasy Rebirth mechanic, there seems to be little fanservice in this game. At least for now... The art style is also quite nice, and I like how consistent it is for every character. The fact they also collaborated with other fan artists and introduced their art in the game through the story card is quite neat too.
One thing that surprised me a little, knowing how fanon can be, is how they decided to depict Eiki Shiki. She has been recently added to Global, and since I like the character, I wanted to get her (which I got, luck enough, in my first x10 prayer). Even if her art makes Eiki look rather average in height, and her battle chibi seems to be a little smaller than that of other characters (LOL), her personality was a pleasant surprise. The game has gone quite a bit with the preachy personality, but, at least in my opinion, her lines also show care and wish for the character to be a good person. Which is quite refreshing from the casual "always angry small girl Eiki who will send you to hell for the pettiest of reasons" fanon got us so used to.
The player-insert part has been done interestingly. I might say this due to not having any prior experience with games where you have self-inserts or isekai, but this one is a little different. First and mainly, there is the part your character is already established to be a girl. Usually, at least from what I know, such games usually let the player pick the gender of the protagonist or make them male, therefore all the jazz and stereotypical "harem" stuff when you have a cast filled with other girls/women/whatever. Then, there is the whole Fantasy Rebirth thing, where, if you go by how some call it - "marry the 2hus", you basically have girl-girl relations. It is funny though how the creators tried giving the protag a bit of personality in the fact that, according to the biggest part of the Lost Word community, she might have a crush on Sakuya based on some of the interactions until now. This comment I have once seen in regards to MC's interactions with the girls in the series always makes me laugh: