Hey, just to answer your questions. IF you design the scene around it to make it blend in more and look more real then it will probably add to the effect of the model, so it would help. But yea, not that much, seeing it will be based on the model. I would just suggest putting the guitar on a white bg and that should be just as good as if you modelled it against a wall. Just you know, the model may look more attractive due to reflections if theres surroundings. You have the idea though, its not supposed to be based on a scene.. but on a specific model, so i will judge all the same .
Question #2, This IS just for fun ... so you will not be scolded if you dont finish .. if you join a battle in the battle arena, and dont finish.. then you may not be able to compete again seeing that there are only 2 competators and then that defies the purpose of a battle in the first place . Your fine modelling that guitar, cant wait to see the progress.. remember though, its a realism competition, so try your hardest to add the realism to it , even model the wrapped wire on the thicker strings .. lol. Cya.