In regards to the blood, it would be hard to know figures. I know of 2 JWs who faced emergency medical treatment, both took the blood required.
I doubt there is anything in the JW lifestyle that makes it less likely they’ll require blood. For example in Australia the JWs love riding dirt bikes as much as the general population, accidents are common.
Also in Australia, you can’t refuse blood on behalf of your minor child, the child will always get blood if the doctors say the child needs it.