Point 1: Well in regards to stealth, it would be hard to know where the resources going to build the ships are actually going and what they are doing, you may SUSPECT what they are doing but you'll never know for sure until they do something.
Point 2: Well as I already said the Icarans during this time were no where near as advanced as they are later, at this point their best sensor tech was Lidar which does not have great range and is relatively easily interfered with. Plus remember the Icarans mainly held the inner most system which means they didn't do much or have many resources in the outter system so if the UN had a colony on one of the outer worlds and simply sent "colonists" they could disguise crew movements.
Point 3: Yep Asians and Icarans still have some tension, although it's less so in those Asians recruited into the armed forces and Fedsec since they are given intensive background and "purity" checks before being allowed to join. (Purity in this case does not refer to race but instead family lineage and loyalty, so basically if your family shows signs of disloyalty your not permited to join the armed forces)
One of the reasons the Spartans (though asian) are some of the toughest and most loyal defenders of the Icaran Empire is in part because they see it as their duty to protect mankind moreso then Icara it's self. Though of course as in any Empire you have your diehard absolute loyalists to the Empire (and a great many in fact).
Point 4: Resistance to foreign powers is human nature yes, but after a generation or so that resistance would either come to an end or there would be none left to resist. Remember the Icarans took nearly a thousand years to expand to control roughly 1/4 of the globe, that's actually a long "Foundation" time for an Empire the size of the British empire and more then enough time to secure provinces that may be more likely to fight.
Well the propoganda value of calling rebellions "minor" is pretty obvious I'd think
Of course there were rebellions and these were brutally supressed by the Icaran armies.
I mean note during the "Minor" Nazi rebellion
Whole Cities were blown to hell by Icaran forces. During it's earliest history Icara was in fact more brutal to traitors then even the Roman Empire which either scared people into being subserviant or brought those who would fight out as they rebelled or resisted.
Point 5: I probobly misworded my statement sorry. The Chinese in this timeframe (Icara's not ours) were already developing firearms in Parallel to the west, they knew how to make guns just not anything they saw fit to put into mass production or use. Just like the real Chinese they tended to be a little stuck in their ways as in "If a sword works why buy a gun?" until they got hit with Icaran guns.
They captured said guns and copied them as best they could, but they still had THOUSANDS of Icaran flintlocks after defeating even a single regiment and they decided to copy them as best they could.
I'll probobly say they had wheel or matchlocks for the most part since you are right Flintlocks are hard as all get out to make. But they still would have had enough Icaran guns to turn around on the Icarans, and a musket ball is a musket ball so that wouldn't be hard to make ammunition.
Granted they'd have a lot fewer cannons as an artillery crew is likely to spike their gun and run for it if they have to.
LOL Well since the real world Nazis loved hiding stuff underground I assume their counterparts in the Icaranverse would use pretty similar tactics for hiding their own rebellious activities
And besides that controlling the dark side of the moon woulda been great till they nuked it lol