I just steamed wallpaper off of our horsehair plaster in our bedroom.

There was an extra decorative strip of wallpaper next to the ceiling that had a kind of white
vinyl coating under it. The white vinyl is still mostly there. It looks like it would be very difficult
to remove that vinyl coating. Right now it's mostly smooth, but it's not uniform with the majority of the wall surface that had no white vinyl on it.

What should I do so that the wall surfaces will all look uniform when painted?

Should I apply anything that covers all the walls before painting?

Thanks a lot, Pete B.