Trying to become the leader of a breast-feeding group as a FtM individual... is a little silly. Belonging to the group is already an infringement on social standards, so asking for a position of power within that group would be pushing boundaries a little too far for the present moment in time.
Trans people aren't very well-understood by cis people, a lot of the time, so this desire for a man to lead a breastfeeding group would be a very strange thing for most. He would end up doing one of two things, mostly, and that would be either reinforcing a belief that trans people are merely confused, or some other thing, or secondly, that trans people like to sensationalize, and try to be like both sexes at once.
I'm not sure that a man could ever be accepted and supported as a breastfeeding group leader. For that to happen, he would either have to admit he wasn't truly a man, or the world would have to abandon their binary-ism in favour of understanding.
As I said, even being a member of the group infringes on people's understanding...
As for breastfeeding itself, though, then all the power to ya. It provides an advantage over not-breastfeeding, so there's an actual reason to do so.