It's hard to give an exact length for the JJK manga as it's still ongoing. But it's been running for a while and has built up a substantial amount of content.
The key to drawing like a manga artist is to observe a lot of manga works. Try copying some to understand the techniques. Also, build up your skills in inking and coloring. And keep exploring different themes and genres to expand your style range.
Drawing manga like Araki involves observing his work closely. Notice how he simplifies complex forms and emphasizes certain features. Try to replicate his sense of movement and composition. It takes a lot of practice and patience, but keep at it!
First, master the basic drawing techniques like figure construction and perspective. Then, study the unique styles of popular manga artists and try to incorporate those elements into your own work. Also, keep practicing regularly to improve your skills.
In general, the JJK anime remains loyal to the manga. It effectively captures the key elements and maintains the story's momentum. Some scenes might be presented differently for better animation effects, but these changes are not substantial and don't deviate from the manga's core.