Are members of the Romulan Senate elected or appointed by the Praetor? Does the Romulan Senate have any real power in Romulan society or does all the political power lay with the Praetor?
How did it work in Rome? Since Romulans are basically space Romans, their governments are likely identical.
It has never been canonically established whether Romulan Senators are elected, appointed, or hereditary. However, we do know that Senator Pardek represented the "Krocton Segment" and was considered a "man of the people," so apparently public opinion can influence a Senator's power. We don't know if the "Krocton Segment" was a geographic location or some sort of ideological faction, or what. We know from DS9's "Inter Arma Enim Silent Leges" that the Senate determines membership in the Continuing Committee, and the Continuing Committee determines the Praetor. The recent novel Typhon Pact: Rough Beasts of Empire by David R. George III, however, establishes that the Romulan Senate is comprised of representatives of the one hundred wealthiest and most powerful Romulan clans -- making it fairly clear that the Romulan Senate is, in essence, a sort of House of Lords, comprised of the Romulan aristocracy. Each is appointed by the clan from which he or she comes, on the basis of the consensus of that clan's members and leaders. Earlier novels, including Vulcan's Heart, established that the Romulan Emperor remains the subject of an imperial cult, but that the Emperor is a mostly ceremonial position -- though particularly venerated Emperors sometimes compete with the sitting Praetor for power. Think of it as being akin to the way a British Monarch would sometimes compete with or exercise power alongside a Prime Minister back in the 1700s and 1800s. However, later stories, including the short story "Blood Sacrifice" from 2004's Tales of the Dominion War, establish that the sitting Romulan Emperor was assassinated in 2374, shortly before the Romulan Star Empire entered the war against the Dominion, and that as of 2383 (Typhon Pact: Plagues of Night), the Throne remains vacant.
Perhaps it's just like in Ancient Rome? Some of the Senators are genuinely elected politicians from the population, and others are "Nobility" who more or less inherit their positions. Romulan "Nobles" would probably be direct descendants of any Vulcan higher-ups who were exiled or command staff of the original colony ships.
It seems like the similarities between Romans and Romulans are not very well developed though. The Roman Empire was not xenophobic, they would often make people they conquered citizens and would try to improve infrastructure of areas they conquered. The Romulans seem to have no desires to do those things. Plus Romulan society seems more set up more like a modern totalitarian state, rather then the old autocratic state Rome used to be. I don't the Roman Empire had a secret police unit, for example, that is a more modern invention. That's why Romulan society comes off as contradictory, they have a seemly totalitarian state, yet it has an seemly elected legislative body. The Roman Senate lasted over a thousand years, how much power it wielded depended on which era of Roman history you want to refer to. Calling the Romulans "Space Romans" doesn't help define them very much, because there are different eras of Roman history and their society is very different during these different eras.