You can start by finding a reliable source to access the manga, like official platforms or authorized websites. Then, take your time to enjoy the panels and follow the story at your own pace.
Well, for reading manga JJK, you could start from the beginning and try to immerse yourself in the world it creates. Notice the expressions of the characters and how they contribute to the plot. And don't rush; savor each page.
I'm not sure about legal places to read it for free with good translations. It's best to support the creators by buying or subscribing through official channels.
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.