You should take a vitamin/mineral combo. I am not sure about the not eating potatoes, rice, sugars thing. Your body needs all that stuff, the trick is to give your body the nutrients it needs in the right time, in the right quantities.
Do not think that such a complex machine as the human body can live on 5 things or something like that. It can, for a while (i.e dieting for a contest) but in the end your body would be sick if you don't vary your diet and provide different nutrients into it.
My two cents.
(fruits don't have all the vitamins and minerals you need as a bodybuilder, and nuts don't have enough fat and it does not provide a wide spectrum of healthy fats...)