that makes you feel strong emotions, it can be drama, suspense, sadness, adrenaline or even horny if you write something sexy, whatever it is but they must be strong emotions, a good writer is a drug dealer
In Wish Fulfillment, I like it when it's about kingdom building and the author makes the protagonist create a utopia according to his or her political ideologies, while other countries with an opposing ideology are backward or dystopian.
Exactly America is very rigid when it comes to comic themes, I'll give you an example, sports ones: Don't you find it curious that some of the best basketball (Slam dunk) and boxing (Hajime no Ippo) stories were created in Japan, when they are not exactly a country that excels in those sports...
1000 chapters is a lot, in my opinion any story you want to tell can be done with something closer to 100 (nothing against long novels of more than 1000 chapters if they are divided into arcs making each arc basically its own story that may or may not be connected to the others).
Revenge, in my opinion if the audience doesn't hate the villain and wants to see him/her die or suffer in the conclusion, then he/she wasn't a good villain or even a villain at all.
True yuri harem are very niche, here I recommend some good mangas
https://mangadex.org/title/676fdcea-1f57-4555-b341-78e4e1fd65d0/tachibanakan-triangle
https://mangadex.org/title/b232c191-6e14-4522-a1a2-c4b0f688f00d/shi-ni-modori-oujo-wa-ikinobiru-tameni-yuri-harem-wo-tsukuru-koto-ni-shita