Q: what is the best starting point?
A: a sketch on the front plane defining the outline, knob handle centerline, mounting points, decorative zones,etc. When adding geometry features, reference and build upon this 'skeleton' sketch.
Q: what commonly features used on it?
A: Extrude Boss/Base for most of the rough shape, Revolved Boss/Base for the handle portion, and I wouldn't know where to begin with regards to modeling all the hand-worked artistic shapes, probably a lot of stitched together surface-type features. The 'art' is definitely the hard part, if modeling it accurately is required. I'd probably try the laser scanner route if I had to do it and see if I could get some kind of geometry to work with that way.
Q:how can I import a photo in Solidworks?
A: 2 ways that I know of.
If you intend to use it to assist in geometry creation, open a sketch, click tools>sketch tools>sketch picture to import an image that you can use to trace sketches over.
If you simply want to decorate your model you can add a 'decals' to surfaces, which maps images of your choice onto surfaces of your choice.
Thank you very much ^_^