Yeah, a corporation owning an entire system isn't really a problem on the scale of the whole galaxy. To use the Disney comparison, Disney's got an effective nation worth of owned real estate and I'll eat my hat if they don't have a private security force protecting assets like Disneyland, but if Disney tried to topple the US government they'd go down, hard. The problem is that the Trade Federation really did have enough firepower to topple the Republic, and without Sidious actively playing both sides to ensure they didn't get the win, they would have. If Disney was operating five aircraft carriers and looking into starting their own nuclear program then they'd be at the point Czerka or the Trade Federation managed.
The secret army bit won't really be a problem under my proposed system because there's no lack of actual armed forces. The clone wars worked because 2 million units, spelled out as being 2 million clones in the novelization, was a massive force that could topple the galaxy and the Republic had nothing to fight with anyway. To run with the Disney comparison again, the US would have a total of maybe twenty soldiers and three tanks in their whole military. It would be relatively easy for some cultist in a small town (or Disney) to collect 50 recruits to build an "army" capable of toppling the US government. Once you plug in sane numbers if makes far less sense for the cultist to be able to pull it off.
Pure Feudalism, of course, isn't the answer hence my emphasis on adding a constitution, bill of rights, and Federalist workings. Fundamentally I think "how you vote" is less important to the stability of the Galaxy than inalienable rights (for aliens too) and a solid constitution with proper checks and balances.
Hmmm, I think with your comparison, the Death Star is something only a galactic level government can build. There really isn't an equivalent to modern day. Star Destroyers/Capital Ships are like tanks to today's world. Someone can build a couple hundred tanks in secret if they have enough money.
The Clone Wars was more about controlling key planets rather than a system by system take over. With hyperspace lanes, there are super efficient space highways in Star Wars. Controlling these lanes, key manufacturing planets, and key resource planets was the extent of the conflict. 2 million clones means less than one clone per inhabited system even at the low end of size estimates for Star Wars.
You actually have this backwards. A centralized bureaucracy will actually end up larger and more wasteful, not less. This is in large part due to how much more difficult it is to hold that bureaucracy accountable. If your city government has an inept department head in its bureaucracy, you have to put pressure on the mayor and city council to do something about it, and that's something everybody in the city can grasp. If that's a federally-appointed position, then your single city will be competing for national attention in regards to that one specific issue.
Good luck getting a Senator or President replaced because what the local head of sanitation is doing. Even in regions where one metropolis dominates regional politics, that'd be extremely difficult.
Now stack planetary, sector, and galactic levels on top of that.
It is honestly hard to say. I suspect that a lot of low level jobs are fairly automated with droids or computer systems. These systems operate more through inertia most likely than anything else. Coruscant itself is very interesting since you literally have super rich people living on top of super poor people. The class divide doesn't get any more real than here. I would suspect a very tiered system and people having 'connects' at least in the middle class. The lower class is just screwed over in the under city. How to fix that......well no idea. Coruscant is just as bad but different than the galaxy as a whole.
Again, you have this backwards. Regulations from a central authority on that scale will make prices and trade worse, not better. Sure, in a more fragmented system, you have some areas where prices are worse, but on the aggregate, individual nations making trade agreements to suit themselves will be better.
The issue is how many corresponding systems said trade has to pass through first. If Corellia decided to tax all shipments through its sector by 0.5% for space traffic control, that is going to be a lot of credits and impact millions of systems in terms of end costs. If every system did this....it gets insane. A good example of this not working are how US States functioned before the US as a whole came to be.
This is not true. Mid-sized and small governments can do so as well, and at the point a corporation becomes a large enough military factor to force a government to submit, it's not a corporation anymore, it's a nation and government in its own right run in a corporate style. And those have the ability to win or lose wars against other nations, just like any other government.
They are a corporation since they are the only entities that can ship enough goods at the galactic level. This is where a lot of problems come into play, since they have a lot of really large ships that need protection, and freedom to travel. Trade is needed since things like Bacta, droids, ships, tibana gas, hyper matter refineries, and various other items are only produced on certain worlds. Sure places can go it alone or a small group of systems, but they are inferior to the abilities and costs of large corporations. It is both a nation state AND a corporation, the Trade Federation had a senate seat as a point of reference.
Even if a government controlled 10 systems, that is not enough to counter a mega-corp. You need 100+ minimum, and even then the trade network, credits coming in from other systems, will allow them to field a larger force than any comparative sized government.
You seem to be ignoring this thing called a 'military alliance.' They are both effective means of defeating enemies (see any number of historical examples, WWII being one of the most easily recognizeable), and are much easier to form than monolithic super-states. Again, use WWII as an example, where the USSR allied with the UK and US, whom it promptly became opponent to during the Cold War for the next four and a half decades.
The issue is that with the size of Star Wars and the 3D nature, it is more like WW1 on steroids than WW2. If each group of systems is allowed to independently align foreign policy, the sheer diplomatic and spying costs would be astronomical. This would force larger blocs to form for protection, with the cycle continually repeating until the galaxy was destroyed or a single bloc triumphed. Unlike planetary warfare, there are no galaxy ending weapons like nuclear weapons to create a stalemate. Any super weapons needs an incredible amount of capital investment, so any government with 10%+ control of the galaxy could reasonably build one, but would drain their economy and leave themselves open. This is why the eventual state of the galaxy would be a single polity, since there is no threat of complete annihilation. Sure the Sith got genocided, but their vast Empire still remained and the Republic gobbled it up, systems and all.