Since Voyager provided the bulk of what was known about the Borg until very recently, that's very limiting.
No, it's selective. I'm entitled to have an opinion on what ideas in fiction are good and what ideas are stupid. None of it is real anyway, so it's silly to act as if we're required to believe it all and have no right to exercise our own judgment or skepticism.
According to Voyager, the Borg have been a space fairing power for thousands of years. But during most of that time, they seem to have occupied a relatively small area, not being on any particular mad dash to conquer the galaxy. This implies they had developed some kind of homeostasis, at least for awhile.
Actually VGR is contradictory on this point, sometimes claiming the Borg are thousands of years old and sometimes that they were a minor power mere centuries ago. Another reason we shouldn't just blindly trust everything the show claimed about the Borg.
Borg cubes are always shown being packed with thousands of drones, and yet rarely are more than a handful of drones needed.
Define "needed." You're only looking at it in terms of physical tasks, but that's missing the point. Drones aren't starship crew; their brains are parallel processors in the hive mind of the Collective. All of them at once
are the Collective consciousness -- that's what a hive mind is. They're always participating in the cognition and neural processing of the Collective, even if their bodies are only occasionally needed for physical tasks.
They'd just grow new ones as needed, perhaps using a species of accelerated maturation like the Ocampa as their breed stock. But they've never been shown to do that.
Yes, they were, in the very first Borg episode, "Q Who." That was the point of the scene where Riker found the incubation chamber. Sure, VGR tried to retcon that as assimilated babies, but that was not the intention in the original episode.
The Borg may not make sense to outsiders but what they do seems to work for them.
That's a nonsensical thing to say, because the Borg have no independent existence. They're imaginary constructs that only work in the way the writers of the story claim they work, and different writers have made different claims about them over the years. And as the audience of fiction, we're entitled to criticize a story that's written badly and unbelievably, and to say it should've been written better.