rax=barracks.
the big point in managing the sling is that you most likely get all or near to all AA techs through it (aside from being first and that rather soon to a new and better gov form).
therefore, much more important than early forces are early explorers. like, scouts or warriors or chariots or horses for the landmasses and especially curraghs for the seas. meet as many AS as you can early, and you have a lot to trade for when you got those slingshot techs.
t_x