We used latex paint and the walls look terrible. I was told to paint them with oil base primer, so I did, but now since dry it looks textured. What went wrong? Do I need to sand before painting again? Can I also latex paint over oil base primer with latex paint?
Most likely you used too thick of a roller, this would leave major stipple (texture) and possible heavy streaks in the primer. Try a light sanding to knock down the texture and reprime. This time use a shorter nap roller.
Yes, you can paint over oil base prime with a latex paint.