Before you start doing that, you need to define your "rules" for Week Number - the ISO specification lays them down very solidly for Monday weeks:
ISO week date - Wikipedia[
^] and is heavily dependant on the week in which the Thursday falls - and as a result an "ISO year" can have between 364 and 371 days depending on the first Thursday of the "calendar" week - meaning that Jan 1st can be in Week 52 or 53 of the previous year, or week 1 of "this" year.
You would need to first work out exactly when your year is going to start, and go from there!