I have pulled off the wallpaper with a mix of fabric softener and water and also vinegar/water, then I rinsed off as much glue residue as I could but you can still see where it was if you look at an angle. I plan to cover it over with oil-based primer then paint with latex paint. The paint/primer under the old wallpaper is kind of rough and lumpy and you can easily see where I have spackled holes and so forth, because of the texture difference. Can I just sand the paint down to make it uniform texture? What kind of sand paper should I use? I don't want to damage the drywall.