The other difficulty with LNs specifically is that, due to the widespread nature of them currently, the difficulty and normality of the Japanese will differ per author. Spice and Wolf is a fairly easy read outside of the economic terms, as both grammar and vocabulary are standard fair. The more “chuunibyou” you go with plot, the more likely you are to encounter the infuriating authors that make up their own jukugo, readings for existing jukugo (usually to generate a nonsense English/German/Latin term in katakana that’s supposed to have the same meaning), and other ridiculousness that bogs down the reading process.
Definitely verse yourself of dialogue-based terms, because, obviously you’re going to find a lot of dialogue in normally character-driven Light Novels. For scenery descriptions, your best bet is to find a longer running series to pick up on the writer’s style and/or read stories of similar genres (most fantasy stories will probably share scenery vocabulary, while sci-fi stories probably won’t).
It’s a shame I never thought of tracking frequency of words I’ve put into my spreadsheets when translating. I may have to start.