One common theme is friendship. Just like in the original series, fanfictions often explore the deep bonds between the Lycoris girls. For example, how they support each other during tough times.
Sure. One great 'lycoris recoil fanfiction' is 'A New Day for Lycoris' which focuses on the characters' daily lives after the main events of the series. It gives a very warm and homely feeling as it shows how they interact in normal situations.
You can try looking on popular manga reading websites like MangaDex or MangaPlus. They often have a wide range of manga available, including Lycoris Recoil.
I'm not entirely sure as there could be many different 'lycoris light novels'. Generally, it might be about some fictional stories perhaps involving characters, a unique plotline, and a particular setting. It could be about adventure, mystery, or relationships within the world created in the novel.