I will leave your question on Aurelian to someone better qualified to answer, and focus on your second question on recruits. It should be noted, though, that by the time Aurelian moved against the Palmyrenes, their queen, Zenobia, had assumed control of Egypt. Not only was Egypt not part of the “gentleman’s agreement” her husband, Odenathus, had struck with Aurelian’s predecessor, Gallienus, it also provided vast amounts of wealth in tax revenue to Aurelian as well as much of Italy’s grain. This was a direct political and economic affront to Aurelian’s regime and thus threatened his legitimacy.

As early as the first century A.D., Italians ceased to provide the majority of the army's recruits. While the Praetorians continued to be largely drawn from Italians, in general provincials provided the majority of recruits for the regular army. During the Principate, the bulk of the army was stationed in the provinces along the Empire’s frontiers, and so recruits tended to be drawn locally. The army also recruited heavily from more rural, peripheral regions, such as Pannonia and Dalmatia. While military life was harsh, it was no more physically demanding than the agricultural background to which most recruits were accustomed, and offered many attractions, such as pay, steady rations, and quality medical care. While it is unlikely the army was, to quote Scheidel, a "demographically 'closed institution'”, the sons of soldiers nevertheless formed an important supply of recruits. As such, during the time of Aurelian, the army had long ceased to be composed principally of Italians.

It is important to remember that Roman identity was not an “ethnic” (the term is anachronistic, but it best fits this discussion) or geographic identity. What constituted “Roman-ness” was highly fluid, and was conceptualized differently by different groups, classes, and regions at different times. An Italian was thus no more Roman than an inhabitant of Gaul, or Syria, or Egypt, even if Italy as a region certainly did enjoy the prestige of being the imperial center for several centuries. From an identity perspective, there would have been no reason for the army to focus solely upon the recruitment of Italians, as being Italian did not automatically make one more Roman. The army as an institution imbued recruits with it’s own conceptualization of “Roman-ness”, which in part served to form close bonds of loyalty between soldiers, many of whom were drawn from different cultural backgrounds.

The Romans had a long history of engaging in “targeted recruiting” from non-Roman peoples, especially from groups with strong martial cultures deemed conducive to producing quality recruits, such as the Batavians. During the fourth century A.D., barbarian recruits tended to be concentrated in specific regiments (which gradually lost this “ethnic” character as casualties were replaced by local recruits), and formed no more than roughly one-third of all field army recruits. Throughout the Principate and Late Antiquity, the vast majority of recruits continued to be from territories inside the Empire. The Romans never, in any period, relied upon non-Romans for recruits.