Answering as someone interested in the job.
1) It's always good to have good reference for a model. As for a bicycle, a high-resolution image of the bike as a whole from both sides would be sufficent. Images dont have to be isometric. Close up of the details, like the gears would be very good too.
2) I would determine the quality by overall accuracy of the model and mesh topology, meaning when rendered the light behaves correctly on the materials.
3) I have used 3x the price of a ready available good quality model as cost for a custom modeling job.