Hi- I have crowns and we now realize that well water was the culprit because it doesn't have flouride. Ask your dentist if a flouride rinse/toothpaste might be good for your son (if he's a good spitter and doesn't swallow it). If so, they can give you a prescription strength one that's better than over the counter.
My childhood dentist seemed to do tons of work on EVERYBODY. Not only that, he was mean, mean, mean. He would start drilling before the novicaine had numbed the area. I wouldn't refer anyone to that jerk.
A second opinion is definitely in order, and the time it takes to do that isn't going to make a huge difference if he only has cavities.
I have heard that the "baby" teeth are very important for the alignment of permanent teeth and that they should only be pulled when absolutely necessary. For a crown, the top portion of the tooth (above the gumline) is ground down to a nub, and the dentist would leave the root of the tooth intact.
Our dentist said to try to stay away from drinking juice all day long, sticky candies, raisins, fruit leathers, etc. as they are all bad for teeth. I have slowly been transitioning to sugar-free candies, and my daughter doesn't say much.... I also have started diluting her juice about 3/4 water to 1/4 juice.
I have a friend whose 2 year old had her front teeth crowned because she won't sleep without a bottle.
Hope some of this helps.
J.