2-Yes there is a main bad guy and he is stronger than Jin and Mugen combined
3-The Sunflower Samurai does not show up.....not even in the end
4-there are 24 episodes and at one point Mugen and Jin and Fuu get attacked by zombies
5-Mugen gets high on weed after smoking it by accident
thats all but none of them are comfirmed its just what i heard