Working Holiday Visa in the Netherlands

Hi!

I received my Working Holiday Visa for the Netherlands today. I have 2 questions:

1. According to the visa, I'm only allowed one entry. Does this mean that if I go back to Canada for the Christmas holidays and come back to the Netherlands, my visa won't be valid anymore because I entered the country twice?

2. This visa is valid for Schengen countries. Does that mean I'm allowed to work in all Schengen countries?

Any information from fellow Canadians who have used this visa in the Netherlands would be greatly appreciated.

Dank je wel!