Given inspiration from this post here, I have been working on a society of aliens in which each tribe lives on a single member of species of enormous megafauna. Let's call the megafauna the "whale" and the aliens on it the "barnacles." Both these creatures evolved on a moon (around Venus to Earth size) that orbits Barnard's Star B using methane/ethane as a solvent rather and divergent biochemistry from creatures on earth. The relationship between these two would be that the whale travels through large deserts to get to the various oases around the liquid methane/ethane lakes that dot the moon. So the large body began to evolve as a method to avoid wasting away as it migrates through the desert. To get even bigger the whale developed a symbiotic relationship with the barnacles (the largest height is around six feet or 2 meters) where they, as detrivores subsist and specialize to eat its waste and provide protection from other large fauna and parasites by taking care of the whale. They build structures on their back and live on it as a nomadic pastoralist tribe. This allows the whales to develop a much bigger size with them being protected from being an easy, giant target and allows the barnacles to specialize in feeding on the waste of the whale and to develop intelligence and sentience to protect the whale, as a result of the vast supply of food they have access to from the whale. The whales live over two millenniums and reproduces barely above replacement rates, and the barnacles reproduce slowly and sparsely as well, living from 400 to 600 years.
So, given the anatomy of the creature in the answer to the linked question by TheBlackCat, and the description and features above, could the whale grow to have the total square feet of the top of its body be at a minimum of three acres (12140.6 meters) to hold a small nomadic tribe to live atop it, and, if not, how large could it get and would that still be enough to have a tribe larger than your average band society?
Here is an image if you need a visual of the creature I am describing: