One ball of Opal sock yarn will make a pair of socks. Jane knits socks for my dad (size 12) and she gets them out of one ball.
There is nylon in the yarn to help them last longer. And yes, you can throw them in the washing machine and dryer. Beth does not look after her Opal socks and they look great!
I have learned something very important during this process. Don't keep anything that you aren't using. Donate it. It just takes up room and makes clutter. It is amazing how much 'stuff' we have accumulated in the past 7 years. That includes yarn :)