Very curious to understand the thinking behind this, why should the weekend be E and A? My first approach would be to have the weekend on D and E which would seem to be the end of the week.
So that the extra day on leap years could be inserted in a weekend while having its own unique number.
So no, the week does not start on Monday, it starts on Sunday.
The name "Weekend" came long long long after Sunday was considered the first day of the week.
ISO says Monday
This only works in English though. The rest of us use the word "weekend" as a block.
If anything, "fin de semaine" would refer to the last working days before the weekend.