Anything that isn’t a voxel / block / chiselled block / fluid / grass is included against the limit: torches, machines, storage, doors, signs, etc.
Each chunk is 16m x 16m x full height.
The limit is 512.
If you position complex towers at the corner of 4 chunks then you can increase the limit to 2048 per 4 chunks.
(The limit only exists to stop players filling small areas with complex meshes that would cause a performance issue for all other players.)