I need to remove oil base paint from drywall. Some areas just peel off, others seem to tear off the top layer of drywall. How do I get it all off?

Bedroom walls have been painted over existing wallpaper and you can see the joints through the paint. How do you remove paper and get a smooth wall to repaint?

I have used Minwax Chestnut on a fiberglass door; I haven’t applied a coating of this yet, can I use a lighter stain to lighten the darker stain as it doesn’t match the other Trim and Baseboard in the house