How to quantify the extent of this water damage?
One thing in your favor is you're not in a hot humid area and you have a better chance of the water from  one-time leak to dry up without mold growing.  The long  stained line you're talking about is a drywall seam that has been damaged due to the water. You should think about peeling the tape off and re-taping it as it won't cure itself. Any areas that have water stains should be wiped down with vinegar as a precaution as it's a great mildew/mold killer and it will soak into the material and kill mold below the surface. After the repairs are finished, prime, repaint and hope for the best outcome. Good luck.