A: For usability reasons there is hard limit of 300MB per model, but you can easily reduce the size of pretty much any 3D model using a simple decimation operator in a tool like Blender, or reduce the size of the model textures (images on the surface of the 3D model) before uploading. Its not so much because we want to be overly restrictive, but simply because 3D models larger than 300Mb makes mobile browsers - especially on iPhones - very unstable and hard to use