Dear David,
I just voted no to the question of whether painting celebrities from photos is considered valid. I admit that when I became interested in portraits I painted celebrities from magazines. I was a teenager then and had no one to guide me at that time. I became quite good at it, and the paintings looked very much like the photos of the celebrities, but it was strictly copying. I taught myself to mix colors to match and that sort of thing. Later, I went to college as a studio art major. We drew and painted from live models. Our teachers made it clear that we were not to use photographs. There is nothing else like it. You observe, converse with the sitter or not, interact with this person, empathize, make choices on composition, color, what to include and what to subdue or eliminate, what is the mood, making countless decisions. It is exciting because there is this living person in front of you, affecting you and vice versa. In a physical sense, this person is a mass occupying a certain place in time and space with air moving around and light illuminating their form, with colors reflecting off their surroundings on to skin and hair and casting shadows. Even in repose, people are constantly moving and resisting gravity. And, they are thoughtful, emotional and spiritual. There are so many levels for the artist to explore about a subject. During the process of drawing, painting, or sculpting a portrait, the artist is searching for much more than a physical resemblance.
I went to your website and saw your work. You have the skills to draw and paint really wonderful portraits. I strongly recommend that you paint members of your family and friends from life and build a portfolio. Potential clients seeing these will know these are "real people" like them. Also, the greatest place to learn about portrait painting today is on the web starting with viewing every single page of every single portrait painter on Cynthia Daniel's Stroke of Genius. Also, go to the ASOPA website (they have been a great help) and the Leon Loard website. There are great links to other sites from these.
www.therp.co.uk (The Royal Society of Portrait Painters is one of my favorites.)
Best luck to you, David.