Assuming your numbers are on and looking only at living space that's less than 2m2 of ground footprint per person, which is impossible, until we start building:
Now let's look at a per person spacial minimum. Kowloon Walled City is widely regarded as the most densely populated site in human history, in 1990 it housed 35,000 on a footprint of just 6.4 acres or 1.3 people per square metre spread across 14 stories or 10.08m2 per person, I think we can do better because those people had to eat and had all their own stuff.
Many modern tiny homes are in the region of 25m2 total living space, but that includes food storage and preparation space we can remove that gets us down to at most 20m2. We get further discounts for communal bathing and storage facilities, and for using everything in three shifts so we can probably get things down to ~5-7m2 per individual without compromising the physical health of the hiveminds many bodies (assuming no external pathogen intrusion). This means huge walk through communal bathes with clothes dropped into a chute at one end and laundered to be put back on at the other, vast fractal bedding spaces, minimal distance pathing for all individuals from bed to work space, if any, to bathes and back to bed each day and everyone moving through perfectly. By the time we take into account access spaces and structural necessities etc... you're probably looking at covering East Asia with four or possibly five stories of living space.
Theoretically that could be in any combination of above and below ground floors, however given the annual rainfall I would look to build the living and working spaces entirely above ground for reasons of sanitation and also to keep spacial loses to maintenance infrastructure (pumps etc...) to a minimum.
Given you're cramming that many genetically identical individuals in that tight if anyone gets a lethal airborne infection the hivemind is doomed before they realise they're in trouble.
