Besides the above, it's important to consider what protocols you're using. Since you said "mesh," I assume you're thinking Z-Wave or Zigbee, but there are different considerations for each. Z-Wave has a maximum number of four intermediary hops. Theoretical range is 100 meters, but that's in open air. In a building, I've seen recommendations for repeaters at least every 30 feet (9-ish meters), though if that's a near-worst case, most devices are likely to get more. But in any case, you'll be limited to some extent. Fewer hops is generally better, but Z-Wave limits you to few enough that it shouldn't be a huge deal either way.
ln the future, Z-Wave Long Range (LR) has theoretical range of up to 1 mile and replaces the mesh with a star topology. If all of your devices are capable of being upgraded (700-series devices can be but would depend on the manufacturer to actually provide a firmware update) or you're able to buy LR devices directly in the future, this may work. Hubitat has promised compatibility (assuming you have a C-7) after the spec is ready.
Zigbee doesn't have a practical limit on the number of hops, though I think most repeaters/routers in the home automation space do specify something (generally higher than Z-Wave). Being a higher frequency than Z-Wave and one that tends to be more crowded (2.4 GHz), the range between hops might be less, but the ability to make more hops may more than compensate for the difference.
But I agree with the above that either of these might not work well in a space that large, so creating two or more separate Zigbee and/or Z-Wave networks and integrating them over your LAN (via Hub Mesh or a similar solution) if necessary to meet your needs may be better.
Another idea: Hubitat can also integrate over the LAN with most Lutron systems, most of which might also meet your needs. Even Caséta, their low-end residential system, can do 2500 sq ft (but has a 75-device max). A "full" RA2 system says it can do 5000 sq ft and up to 200 devices. If you feel like paying out the nose for even more, they've got higher-end residential options too, and a variety of commercial solutions that might be more appropriate if your building is commercial, as stated. None of these are cheap, but Lutron has a solid reputation, and so it's an alternative that might be worth considering. Again, it can integrate with Hubitat, though depending on what you want, it can also be a perfectly capable system on its own (though Hubitat can do quite a bit more).
