I started at SJPP at the end of Mar, arriving in Pamplona on Good Friday. The path from Roncesvalles was fairly busy, and remained so for the Easter period. There appeared to be a combination of youth groups, family groups, etc, although I don't recall seeing the larger groups in the albergues that I stayed in. By the start of the second week, the crowds were gone and weren't an issue again until Sarria.
Walking conditions were mixed, but there seemed to less than the average number of rainy days, so I guess I was lucky. I carried long thermals, but didn't need them and personally wouldn't take them again but rely on layering with rain pants, rain jacket and a light fleece to augment my normal trekking kit.
Read the threads on rain gear. I carried a rain jacket that was able to be used as part of a layering system, but would also consider a poncho as an alternative.
Regards,