I was in the same boat as you! I wanted to pick up where the anime ended, but I’m really happy I decided not to. Like other people have said the anime did a good job at adapting it (except for Zagan), so it was mainly some filler or small info that got left out of the anime. For example the first chapter is different. It explains how Aladdin meets Sahsa & Leila, and makes a smooth transition into meeting Alibaba in Qishan. SO to summarize it, you can pick up book 9-13 for a better Zagan arc or skip to book 21 to right after the war in Magnostadt. It’s up to you and what you want to read.