A few more megapixels won't hurt if you're really after a quality photograph of art work. I'd try to stay away from superzoom or point & shoot cameras - their quality isn't up to snuf.
There are some very good used cameras on the market that can be had for an affordable price with good interchangeable lenses that will make an exceptional print without too much, if any, noise in the prints, which is what you really are after.
Try to get at least 3200 ISO as a top limit for low light if you're shooting in natural light. Some museums or galleries aren't especially too well lit, and if you can, customize your color balance for the right color in your prints.
You're right to use a tripod for any copying of any artwork, no matter how large or small so that you can stay at the lowest ISO with the best depth of field. If you can't use a tripod, you'll welcome the extra ISO for handholding the camera. Some cameras have a lot less noise for higher ISO's - check the comparison charts and reviews.
Finally don't shoot at too wide a zoom or you'll get barrel distortion - don't shoot from too close. Good luck!