I had hoped others, too, would reply to this topic. Alas!
Anyway.
Tiberi (the vocative case of my nomen is simply Draco, btw), these periods have been selected by none other authority than... me
. Kidding.
The Kingdom is the legendary period of the Roman kings such as Romulus, Numa Pompilius and the Etruscan kings such as the infamous Tarquinius Superbus. Most historians seem to agree however that around the 8th century BCE Rome was still more of a grouping of villages than it was "the Urbs". There is also still a lot of debate as to how deep the Etruscan influence went. Piscinus, if I get this correctly, contends that Rome and Latium were part of a larger cultural network which was influenced by Etruria but in turn also influenced Etruria itself.
The Early Republic starts in 510/509 BCE with the chasing away of the last Etruscan king (allegedly a hated tyrant) and the wars against the Etruscans. The most notable of these is the war against the Etruscan general Lars Porsenna, connected to the tale of Mucius Scaevola and his burnt hand (in reality, however, Lars Porsenna probably defeated the Latines). The Early Republic is characterised by an oligarchic, patrician rule. Conversely, in the Middle and Late Republic there is an evolution towards plebeian emancipation. The office of Tribunus Plebis is created and later one of the two consules has to be a plebeian. I don't know all the dates and facts from the top of my head though.
My division of the imperial period is fairly straightforward. As the early principate I consider the Julio-Claudian dynasty and the Flavians. The Adoptive Dynasty would be the middle principate and the rest up until the tetrarchy of Diocletianus would be the late principate. I divided these eras along the lines of dynasties and types of government, mainly.
Valete,
Draco
Gn. Dionysius Draco Invictus