I'm in the process of removing wallpaper from my master bath. After removing the paper, I found large portions - but not entire sections - of the walls were skim-coated & not primed before wallpaper was hung. I'd rather not get into washing all the skim-coat off. Is it sufficient to lightly sand the skim-coated portions & then just spackle/smooth the edges before priming w/ oil-based primer?

Any help is greatly appreciated!

Yes you can sand and spackle the edges to smooth out the walls but it depends on how good of a job was done before as to how well you will be able get the walls smoothed out. If you have gotten all the glue off of your walls you don't need to really use an oil based primer as an acrylic will work just fine.