Anytime you paint a wall or paneling with white or light colored paint you will always create a cleaner, bigger looking space. If you paint knotty pine paneling be sure to seal the knots properly before painting. If you don't, the paint will not saturate the knots and they will bleed through.
That's a tough call. Men usually love it, women usually dislike it. I think it depends on the light in the room. You should hire a realtor with staging experience or one who can refer you to an experienced stager. They will point you in the right direction. If you have any questions about this, call me, my cell is 714-7724.