Posted a month ago and got no responses at all.
All the sources I'm getting on "Roman government" are about the government in Rome. I'm looking more for information on towns like Pompeii and Ravenna, larger places rather than small forum/market towns. (Capua specifically, but most of the sources I'm finding there are in French.) Pre-CE info, please.
I've found references to "duumvirs" who were "usually in charge of towns", but not much more. Were there aediles and praetors, like in Rome? How powerful and numerous were the magistrates?
Short answer: it varied depending on the status of the city, but most coloniae and municipia had a popular assembly, a 'senate' made up of decuriones, and four executive magistrates (two duoviri and two aediles). The four magistrates rotated annually, and were probably almost always drawn from a small pool of decuriones in most cases.
Capua, at least in the 2nd and 1st c. BCE, was different. Capua had been very naughty during the 2nd Punic war, and had opened her arms wide to the invader Hannibal. For this, Rome was very displeased. Capua was eventually besieged and retaken by Rome, after which its status as a self-governing town was revoked. The "ruling class" (read: nobility) was practically annihilated, and most of the land was re-branded as ager publicus populi Romani, in essence land belonging to the Roman state (in practice, Roman aristocratic cabals wound up controlling a lot of it). The Senate had plans to "deport" Capuan and other Campanian malcontents, but it isn't clear that this was ever carried out. The region remained very prosperous. At least some of the old Capuan land holdings went into the founding of the colonies of Volturnum and Liternum in 194 BCE. The town itself survived and even thrived, but was ruled by a prefect sent from Rome (Livy 9.20.5 26.16.10). Sulla sent veterans to live at Capua in 81 BCE, then Brutus Rullus (tribune 63 BCE) tried to found an official colonia (of 5,000 civilians) there. Cicero argues vehemently against it (Cic. de lege agraria i.6.18; he specifically mentions the Capuan betrayal to Hannibal, and how Rome should not want to reward such a place with colonia status). It isn't clear if the 5,000 colonists ever actually arrived at Capua in 63. Four years later, in 59, Caesar did in fact put a colonia atop Capua, this time made up of Pompey's veteran soldiers. I'm unable to find a good source for this action, but L. Piso was there in 58 as a decemvir (member of a council of 10, probably in charge of organizing the colonia land, but I'm not sure on that).
Edit: Brutus for Rullus, wrong Livy citation, and miscellany
I don't have any information on Capua but Pompeii specifically had two aediles and two duoviri. The magistrates were in charge of the town and the main city rarely got involved in local matters source. Is this what you were referring to when you asked about how powerful they were?