If this piece is pretty much a straight-on view, place a guide-line right in the centre of the photo so you can save yourself a bit of work in the long run. That way, you can focus on just one side for now and once that is done, flip it over and edit.
Start the line art. Do what you’re used to doing. I personally don’t use strokes in Illustrator because I like to have more control over my lines, but honestly, do what you feel the best at doing. I like to start from the eyes because that is the most central part of the illustration. Then just build around it.
As you’re illustrating your piece, explore some ideas in shading, or just add to it. I would never suggest copying the piece straight up, but allow yourself to be creative. Also, don’t rush it. As you’re only focusing on one side of this piece, you’re already saving yourself time. Let the lines flow and add your own perspective on the piece.