Well, I'm not entirely sure as I haven't read it specifically. But generally, a 'princess slime' light novel might be about a slime that has some sort of princess - like qualities or a story centered around a slime princess. It could involve adventures in a fantasy world, interactions with other creatures, and perhaps a journey of self - discovery for the slime princess.
You could try checking large online book retailers like Amazon. They usually have a wide range of light novels available, so there's a good chance you'll find 'princess slime light novel' there.
Well, one obvious difference is the medium. Manga is visual, so you can directly see the slime's appearance, the expressions of characters, and the action scenes. For example, in a slime battle scene, the manga can show the slime's movements vividly. However, a light novel uses words to describe all these. It might describe the slime as a gooey, translucent blob that pulsates with a strange energy.
Well, without more context, it's difficult to say exactly. 'Slime' in light novels often refers to a type of creature, which can have various forms and abilities. The '300' might be a volume number, a chapter number, or something else entirely. It could be a story where the slime is the protagonist and there are 300 important elements in the plot, like 300 quests it has to complete or 300 different types of magic it encounters.