well your only GM actions could be as simple as:
-control optimus in general and with it play as the autobot leader as best as you can
-give your opinion if I were to ask stuff for the rp (mostly small stuff (this is mostly though PM))
-for plots I can send you something that has to happen IC from optimus at times that you have to include one way or an other.

you dont have to accept CS's, that is pretty much my task
you may but are not forced to check up a little if people dont go all over board and break rules or something (i know I have not really put up any rules but its pretty much the same rules found everywhere), mostly that would be stuff to keep peace, but as said, that is optional.

the Co-GM actions in this rp are basically to dived the leader roles between a few players so they are not all controlled by the same person, and give me some support when I am unsure of some stuff (to what I just ask for your thoughts)
only reason its a co-GM is because the leaders are pretty damned important and are needed to start some plot stuff at I guess regular moments.