You should add in a mayor power in decline which desperately tries to regain it's old glory, or something else that could give political interesting conflicts.
Hmmm ok, so this major power is on the decline it's falling apart and desperately trying to get it's act together, maybe some kind of monarchy, but a throne is a little cliche, so let's go with a regent.
So the Regency consists of a number of city states spread a across Salmoneus, possibly one or two colonies on other worlds as well, it does not have power of all of Salmoneus and there is a couple of regions which have claimed independence from the Regency.
Every city state has a council of a size dependent on the city and can be as small as 5 and as large as 48. New council members are elected by the remaining council members when they die, they always try to maintain their council size. There is no law distinguishing the common man from noblemen, however councils always keep themselves to the high classes, if you are not well established you stand no chance of being elected.
Every city also has a patrician and auditor, the patrician is effectively the only one who can pass laws in the city regarding land and tax, he/she also has the ability to overrule anything the council tries to do although he cannot pass laws without the councils approval.
The auditor is the commanding general of the city guard. The city guard is both military and police force.
Auditors are selected by the patrician, usually the patrician will select a new auditor upon arriving on their position, but it is not unheard of for them to select the same one. They are usually selected from the city guard but since the auditor effectively functions as the patricians right-hand man it's not unheard of for the patrician to opt for someone more trustworthy. While the auditor has complete control over the city guard, the patricians orders go above that of the auditor.
Patricians also take a place in the grand council, the grand council selects the next regent, they don't need to select the regent from the grand council itself but they usually do, they determine such things as state boundaries, council sizes and various disputes between cities.
The regent has the same power over the grand council as a patrician has over a council, with one difference, a patrician can pass any law without the grand council's approval.
Every time a supreme auditor dies another one is chosen from amongst the auditors by the auditors with little interference from the patricians and regent. Although patricians my pressure their auditors to vote one way or another, ultimately they have little influence over the vote. The supreme auditor has no control over the forces of the cities, instead he/she has control of the regent guard which is based in the capital and is twice the strength of any other guard. Again the regents orders go over the head of the supreme auditor.
How's this sound? I'll go into greater detail and work out the cities later, there should also be a number of rogue states on the fringes of the regency on Salmoneus.