nearly all correct - but its not 1 voucher per day per person, its one voucher per night booked, so in your case its a total of 4 vouchers per person.
face value - adult vouchers have a different value to childrens vouchers, and the face value of them (in euros) is printed on the back of the vouchers. If you paid for your vouchers in euros, then yes, its exactly what you paid for them that is the face value. If you have paid for your vouchers in pounds sterling, the value of the standard vouchers is around 25 euros for the adult voucher, and 11 euros for the child voucher. But again, when you get to your hotel and collect your half board vouchers, you'll see the face value of them (in euros) on the back of each voucher.