How to repair damaged lining paper for painting?
I had exactly this in one room in our house. I simply treated it like a normal wall, filling the holes and sanding until flush. 

For the scratches, you could probably just paint over with a 50/50 paint/water mix to seal the fibres, and then sand and fill as necessary when dry.
I find Quick-Dry PolyFilla perfect for light surface scratches. It dries so fast that you can do two or three fill &amp; sand operations in about half-an-hour.

NB:
Make sure you've sugar-soaped the wall really well, as any residue wallpaper-paste may cause the paint to blister.