Portrait C&C very welcomed

Your D7000 has the same sensor as my K5's so don't be afraid to increase your ISO a few stops.  I'm sure your 18-105 will do just fine, you don't need to spend.

The advice to "go long" is sound.  Using my Tamron 28-75 (highly recommended) , its out towards 75 and  if I'm using my 50-135, it's out towards 135.  I looked at some recent head shots and the shortest I got was 63mm and it was a very intimate composition.  A longer focal length will flatter your client.  Tons of explanations online.

Also, don't ignore a good window if you have it.  Window light can be beautifully soft, very flattering.  Add a reflector and you're in business.  Plus it's WYSIWYG constant light.

This was done with a window and reflector at ISO 800: School of Titian .