180km² is extremely big, why not go smaller to begin with? Even games like Skyrim that seem huge are not that big actually, I think it is 5x6km or so of playable area, which is only 30km². So you see even big companies often chose smaller world sizes, because of performance reasons and because of costs, since the world has to be filled somehow. If you want bigger terrains you have to use trickery to make it work with good performance.
If you still want to do it, here are the limits of the engine: The biggest working heightmap by default is 4096x4096 which results in a 16km²world, a 8192x8129 heightmap should work as well, since modern hardware is capable of using that big textures, which results in a 64km² world. You can also vary the square size in Torque, normally 1 pixel is one meter in the game world, but the larger the square size is, the more chunky and low resolution the terrain gets, my personal limit is square size of 2, but it seems you can also use numbers like 1.3 etc. So the biggest possible terrain in Torque without getting too ugly is 8192x8192 heightmap with square size 2 which gets you a 256km² terrain, in case you get 8192x8192 textures working.
You can also stitch multiple terrains together, which would then lift all limits, but there is an ugly seam at the edges, someone coded a solution for it, search for "Torque terrain stitching" or so, you may find it, but no idea how complete it is. Alternatively you can just cover the seam with water, objects, mesh terrain, or by just mashing the terrains a bit into each other so the terrain meshes intersect a bit. But I would try with a 64km² world and see if that is enough, I once did it and it is extremely huge. Performance is not the big problem with the terrain, it depends more on how much more you add to the terrain.