I should probably let you know what sorts of troops are already under the Imperial banner. Currently, your army is composed to a large degree of mercenaries: Russian, Georgian, and Frankish spearmen total about 20,000, plus about 10,000 light infantry, mostly Crimean Goths and Bulgars. For native troops, you have about 8,000 each of skutatoi (pikemen with archers mixed into the formation) and menavlatoi (lightly armored men with heavy javelins). The Varangian Guard number roughly 3,000. In the cavalry sphere, you have about 5,000 Pecheneg horse archers, 8,000 light and medium lancers (mainly Khazars and Alans) and 4,000 Imperial Tagmata heavy cavalry with bow and spear, plus a few hundred Norman and French knights.

This doesn't count the troops raised under the theme system (sort of like a Byzantine feudal system, with local leaders contributing troops to the Emperor's command in an emergency). In a pinch, you'll be able to draw on some of them as well, but you don't have much control over who they recruit or how they train them. Most will be of low quality.