Welcome to the family, Susan!
You may very well meet others who are walking for the same reason as you, or for similar crushing losses - and there is much sympathetic company on the road. Yes, there are lots of people who are on a holiday, but many more who are walking for 'other' reasons and who will be quite open to sharing a deeper conversation about this mystery of life and death that we all have to face, at some point.
If you start in March from SJPP, you will have to take the Valcarlos route. This is the more historically authentic of the two routes to Roncesvalles and it is
gorgeous. There are two options: to walk to Roncesvalles in one day or to spend the night in Valcarlos, and then on to Roncesvalles the next day. I've only gone this way in early March, and there was snow at the top, but not too much, though we did have to walk down the road from Ibaneta. As others have said, layers are important as it can be pretty chilly in the mornings. I find
most important to be gloves and beanie.
The pics here from my March-April walk in 2015 (at the same time as you will be going) give you some idea of the weather. It was everything, from glorious to truly awful.
Edit - It's impossible to generalize about distance and the number of walking days.
Right before turning 60 I started in St Jean on March 11 and walked into Santiago on April 12, with 2 planned rest days, and 2 really short ones after a fall. But your distances are
yours! Take your time, and remember to pace yourself, especially in the first week to week and a half.