Number of cameras is more a function of the 'complexity' of the object rather than the size.
Easiest way to find out for static items such as bikes and sofas would be to experiment with a single camera.
Never tried a bike, but I think it would be hard to get a good scan with any configuration since the complex details are on a very small scale relative to the size of the object I.e. spokes, cables, frame etc. That means you will need to get close, which means depth of field issues, and also loads and loads of photos to get the coverage/overlap. Occlusion will also be a problem more on a bike than a sofa, and registering the left side of a bike to the right side will be tricky as when you get round the front/back there isn't much bike to look at. The biggest problem with a bike is that they tend to be shiny, so start with a muddy/rusty one!