Should I stain my cabinets a dark brown?

If you stain them a dark color it will make the room look smaller. You can sand and refinish scratches with a very fine grit of paper, clean with a tack rag and then apply your finish. You will find that several brands have a polyurethane in them that will protect the cabinets for long use. Best bet would be to match your existing wood work such as trim and even carpet, take samples in to a local hardware store along with a door front from the cabinets (one that might have the most damage) and have them give you a good opinion of what can be done. Good luck.