Answers to questions
1 Obito was not there dead, he was in coma, and madara game obito his left eye back, since he had bz take over his body, will all that a pair of dojutus eyes are better than one that's why he has it
2 sage of the sixs path did not just appear to them, it when hasirama applies his chakra on madara's half body that d sage of sixs path used as medium to communicate with d hokages,
3 d half body was d part that sakuke cut off, before madara entered d dimension, and yes madara regenerated his body back.
4 one of the questions for ages, how obito followed other people who use dimensions like minato etc, he waits until they open/ use their dimension and then synchronise and get to that location or use what is left of their essence before d they went into the dimension and synchronise with it.
Questions to be answered: how did obito locate people, and move to d location without no detector or compass, or markings
Doubts didn't we all see madara pick one of the wz and add his chakra making that part of wz become bz
Doubts bz said when madara cultivated hashi call it or madara meat or mixture, that zetsu accidentally came out, how then did he release them