Throughout much of the CK era, the Roman army relied on the themes. Each theme had a central core of professional soldiers on the imperial payroll (which paid a big bag of gold to the strategos or dux of the theme who then used that to pay the proffessionals). These proffessionals were typically from well-off families. How else could they afford the horse, weapons and armor?
The bulk of the theme armies were, essentially, conscript farmers. These men would only be called up in a crisis, otherwise they were free tomoive their lives. They'd likely be provided with basic armor and a weapon, paid for by their family (if able) or community (equipping a solider was part of the community's tax obligations) occasionally by the empire.
Finally, you had the tagmata. These were full time soldiers in the direct employ of the emperor. Some, like the Scholai (the elite cavalry of the army) were usually native Romans. Others (the Varangians) were foreign mercenaries.
If all this sounds sorta like the composition of a feudal kingdom (noble knights, peasant levies, king's retinue + mercenaries) you've been paying attention. It *was* compositionally similar. The difference in mainly that all the gold paying for this went through Constantinople first, before being sent down through the domestics and strategioi.
So how much of the Byzantine Roman army was a professional? Probably about half. And of that half, a large chunk of that stayed in Constantinople. E.g. the Numeroi, whose ~4,000 men manned the Theodosian Walls with support of contingents of the other tagmata. This "home army" also acted as the police for the queen of cities in-between sieges.
At its peak, the Byzantine army probably had around 60,000 combat soldiers (plus an equal number of support staff), and maybe half were proffessionals and half of those were field troops and half of those stayed in Constantinople.
By extension, a field army of 25,000 (roughly the biggest army Constantinople could muster) would likely be about half professional. Less pros and more scrubs if it was a defensive battle in the themes. Infantry are great in the mountains. More pros and less conscripts in the offensive wars to retake Antioch, as the open land of the Levant is rewarding for cavalry and risky for infantry.
TL;DR: An accurate Byzantine army would probably be ¼ retinue, ¼ men at arm's, ½ levy. Some of that retinue would never leave Constantinople.