Does the first week of Nissan have a minimum number of days? Or does it range from 1-7? If it does have a minimum (greater than 1 ..obviously), why?
The Shulchan Aruch (OC 428:2) informs us that under the current fixed calendar, Rosh Chodesh Nissan will only fall on either Sunday, Tuesday, Thursday, or Saturday. So there can be weeks of 7, 5, 3, or 1 day respectively.