Taking a planet, and policing a planet, are VASTLY different operations. A few guys throwing asteroids can take a planet. Policing that planet would likely take around one operative per 100 population.
Throwing asteroids is more "destroying" than taking a planet. If you wanna take a planet it's nice to be able to do something with it afterwards.
Sounds like someone needs a rock dropped on them.
Neither the Republic nor the Empire had the habit of "taking" a planet. The Republic was a federation of almost independent planets, and the Empire used the same structure with just a random intervention here or there if one tried to actually act independently. And the Empire interventions were much more on the lines of "destroying" than "taking".
We also saw clones and Jedi working with local security forces very often.
This drastically reduces the number of operatives required by turning it into a security force assistance mission.
psssh , I never saw any belter boots on Earth
You wouldn't need to police the planet, just control near space.
A half dozen orbiting gun platforms equipped with ground level sensors could destroy any ship leaving without permission.
So... like... some kind of blockade?
Depends on your stance on genocide
If you want to take a earth-like planet and keep the population in tact, you need a ground force in the hundreds of millions. Don't underestimate the entrenching capabilities of an entire planets. Orbital strikes will only get you so far, if the enemy has anti-spaceship submarines and man-portable low-orbit missiles (check out the starmoth setting, seriously, do it)
If you don't care about the population, but want to recover the planet, you could just put up a blockade and a statite parasol and wait a few years, until the perpetual winter and darkness has reduced the population to a few hundred thousand(targeted strikes on energy infrastructure to speed up the process), and then sweep in to mop up the remainder. It's gonna take some geo engineering to recover something resembling an ecosystem, but that's manageable given enough time
