> Is there enough time in the lifetime of a star to build and use those structures?
If a brown dwarf, most certainly
> Are there plausible social arrangements stable enough to last the duration of such a project?
Could just be an unterminated machine process initiated by living beings at some point
> Are there intelligent beings with a drive to limitlessly expand their population?
This one, I agree. I think once we start expending enough we'll realize there's only so much that extra matter and energy will get you and it doesn't bring you closer to "solving" the universe or escaping it and you just stop going for more.
If a brown dwarf, most certainly
> Are there plausible social arrangements stable enough to last the duration of such a project?
Could just be an unterminated machine process initiated by living beings at some point
> Are there intelligent beings with a drive to limitlessly expand their population?
This one, I agree. I think once we start expending enough we'll realize there's only so much that extra matter and energy will get you and it doesn't bring you closer to "solving" the universe or escaping it and you just stop going for more.