traits and Consuls

[QuintusSertorius]

Praetors can lead armies by themselves, as can anyone deputed to lead the army by a magistrate with Imperium.

Technically a praetorian army is half the size of a consular one. But if that praetor is the gevernor of a province, he'll probably have more than that at his disposal.

As to going beyond the term of office, in emergencies a magistrate might be prorogued for a year or two. Also once a consul had served their term, they went out to govern a province the following year as a proconsul. If you think that's too brief to do anything, that's kind of the point.

The whole system was designed to prevent any one man becoming more powerful than all the others, which is why there were at least two of every office (the consuls were supposed to exercise power on alternate days, for example). It's also why many provincial governors would provoke wars with local tribes and aim for a quick victory and peace treaty within their year. There was always the fear someone else might come and replace them as governor, and claim the spoils and glory.