It doesn't make any sense for Toriyama to direct the FFVII remake. For a true FFVII remake, the important (or all) staff members who made the original JRPG must make a return like Kitase as the director, Sakaguchi as the producer, Uematsu as the composter etc.
I think Toriyama could direct the FFVII remake, the game story was already writen since 1997 and if you are worry abou the ""linearity"" ,he practice with the FFXIIsaga. Another candidates for director could be Yoshinori Kitase, Hajime Tabata, Tetsuya Nomura.
As for producer i don't mind so much but i think that Sakaguchi is
not a must here, cause the role(what i know) of the producer is to look after the budget ,limiting or allowing the director to do certain thinks if it does high too much or not the budget.
The music, Uematsu only for remaking the ost but if for some reason they decide to make a whole a new ost i would like either Yoko Shimomura
or Takeharu Ishimoto/Masashi Hamauzu(FFXIII ost was
)
As for the battle system they could reuse the one used in the original game or they could make a new one although i would like that they stay away from traditional turn base, active time battle,conditional turn-base battle, active dimension battle or any battle system that follows the "wait X time to perform Y action"(i could accept magic actions as the exception but not the regular attacks) I would like more the real time battle from the online FF or FFXV.