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I do some of that kind of work - shoot paintings and create giclees for artists. I use the 100 f/2.8 Macro lens. I put up a neutral background some distance behind the table where the painting is set up and include a gray card in the frame. It's important to seat the painting as near vertical as possible and light the whole surface as evenly as possible. (If necessary, you can suspend the painting on wires from above; also, if the painting is just a little off vertical, you can fix the perspective in Photoshop). Normally you want to avoid picking up reflections off the varnished surface.
You shouldn't have a problem enlarging and reducing the image for different purposes.