Please don't try to trick people, it was completed when you made that post. The raw page clearly has chapter 34 (Released 2025-04-07) marked as the final chapter, even the mangaka's twitter has a pinned post about volume 6 being final.
They can seal area off as it's in fixed location, the mascots can't leave the grounds and it's passive unless someone enters it. So it should count as 'safe' under the containment guidelines. (Note I'm just going by what's presented in chapter, haven't read the full JP article)
Why would you eat a 5 days old burger and sandwich which are definitely spoiled and will make you sick (thus lowering chance of survival), when there's packaged preserved foods available.
I think it's like a pennant banner, they're cutout images on a string, the point being she couldn't get a real plate between the bars. Could possibly be referencing that magic trick where you pull long chain of handkerchiefs out of sleeve/pocket/mouth.
EDIT: Apparently a reference to Lupin
It was to make them think he had to put a lot of effort into getting them a special one-off exception, and indirectly threatened that if they share that fact publicly on SNS, they'll get in trouble for it. So he addressed the bosses concern about other people learning about the exception and...
In case anyone wasn't aware, there was some recent news, the manga will be getting published on a new site that launches on October 17th. Whether that means a new chapter or not remains to be seen.
He was most likely talking about a 400oz one which is currently worth roughly 1.5 Million USD, hence comparing it to the cost of building a nice house.