The main plot of 'dororo' is about a young samurai named Hyakkimaru. His body parts were sacrificed by his father to demons in exchange for power. Dororo, a young thief, accompanies Hyakkimaru on his journey to reclaim his body parts from the demons.
It depends. Sometimes mangas continue their storylines after the anime adaptation ends, but for Dororo, it's not a straightforward yes or no. You'd have to check the latest updates from the creators or official sources.
The Dororo anime doesn't cover the whole manga. Some plotlines and details might be left out or adapted differently to fit the anime format and runtime.
A common theme is friendship. Dororo and Hyakkimaru's bond is often explored further in fanfics. Another theme is redemption. Since many of the characters in the original have complex pasts, fanfics may delve into how they seek redemption for their actions.