JVS doors just remove collision when opened (however some have dts model collision(which also collides when they are ghost bricks)) and the default doors have less than 10 collision spaces?
i'd say you would only be limited to 10 cubeish bricks
Most JVS doors have no collision models at all. The "collision" is handled by the brick it is attached to.
Also, making a 100k+ build into one brick won't magically make your computer handle the build better. Brickcount is an issue because of the number of faces. That's why Badspot and kompressor implemented a brick system where unseen faces get removed. If you just made the build one brick, you wouldn't get any benefits other than being able to plop 1 cityblock, as the face count would remain the same, unless by some technical
tour de force you manage to simplify the mesh to make it fit your needs. But then you'd have the problem of retaining the textures, which would only work by generating and mapping a texture to it. The only way it could work would be making it as a print brick and then using that texture as a print.