infantry... I have 28 legions, following lerasian organization. Im pretty sure its 10k a legion... As for navy, varies, and depends on how much profit the AOS makes. Air Force is limited, I have forgotten to assign numbers to it.
Lucky. I recommend lots of diplomacy, including bribing small countries into becoming your vassal by giving them tech for their military. However, my vassal broke free and is currently under siege, but has not responded to war posts.