It'd be almost impossible to police, although you could in theory do it. An apartment building can have its main doors locked and bolted and guarded by a few police and that might trap hundreds of people.
In the short term it might work but if people start literally starving there's one tool that Americans are more likely to have and might start using. It would be total chaos.
I mean, house arrest is less about guarding the doors and more about catching people out on the streets. Plus, you'd secure the stores (which are deigned to be locked up) to discourage people if you wanted to lock up an American suburb.
Yes. It's happened before. After the Boston Marathon bombing there was a "shelter-in-place" order given that prevented anyone from leaving their homes, and subjected residents to military rule (including door-to-door warrantless searches).
Pretty much. In the Uyghur concentration camps they regularly gather up the victims of the camps and have them watch beatings and brutal rapes. I've read that in the testimony of several escapees from the camps. That plus everyone gets "minorly" tortured for not learning Chinese fast enough or minor transgressions like looking away/closing eyes/crying when told to watch a beating.
