Upload & Sell: Off
Well..............you can use ANY lens you want for portrait photos as long as you like the effect. We have a really cute poster at our dog club of "doggy noses" of different breeds taken with wide angle and ultra-wide angle lenses. Different and fun, and therefore worthwhile as everyone who comes in has to chuckle at the shots.
On the other hand, and relating my experience only, generally something between 50mm and 85mm gives the best rendition and proportions of the head/face without foreshortening or distorting the features. This length range also gives you more working distance, which seems to make it easier to handle and pose the pups.
At shows when shooting portraits I generally use either my 85mm or my 150mm, valuing sharpness over all else.
I am not sure that the body you use is that big a part of the equation as long as you are familiar with its specific features. If anything I would end toward a body with higher usable (low noise) ISO and the ability to shoot at a frame rate of at least 5 fps. Just about everything Nikon has today fills that bill, more or less.
Most importantly.......just shoot - shoot - shoot. That's the key.