Here's my take on the subject.

You will have ten Cyrodiilic legions as your standing army, numbering to roughly 50000, the largest regular ground force of any nations. They are professional troops that you can deploy anytime, obviously with the restriction of traveling time and logistics. Otherwise, you can have more numbers in other armed forces, such as the Penitus Oculatus or local militias. These fighters are not regulars, in the case of militias, they will rely on citizen soldiers, which means they're not as skilled as the legionaries and takes time to mobilize them. Groups like the Penitus Oculatus are obviously not front line soldiers, though they could be used as such. They will trade heavy equipments and numbers for even quicker deployment than the legions, essentially, they're similar to CIA's SAD. 

You legions should be mostly infantries, with organic regiments of cavalries and battle-mages attached to each legion. They are comparable to how the Romans organized themselves, with any fantasy elements serving not as primary units but as support to the main force (again infantry).

High Rock is fractured and mostly independent for its defense. Each of the five realms in HR provide its own military, and fight quite differently than the legions. I presume there are local recruitment for Breton legions, but their numbers are much lower than their Cyrodiilic counterparts. I am thinking at most two Breton legions, with a greater focus on magic due the Bretons' natural affinity, totaling to no more than 10000 there.