I start May 7. Am buying a new sim card when I can, only once in Spain. I was going to pack a poncho but decided to keep with a rain jacket and now, just waiting for a new rain kilt to arrive. The kilt is simply plastic with a velcro belt so it can be used for a number of things as needs arise. Basically, the jacket, ( that can be worn with a fleece sweater and keep me warm down to 0C), and the kilt are lighter than the poncho. Use of a pack rain cover is also used when walking thru cities to disuade anyone thinking they have easy pickings from pack pockets.
On the choice of route, let the Pilgrim Office help with that. An option that avoids all mud is the Valcarlos roadway. On the Napoleon Route, there is 7 km where mud is unavoidable, and once past Cize, do take the RIGHT HAND path. The marked path to the left is extremely steep and if wet, courts disaster.
For me, Valcoaros, 12 km first day and 12 km second day, or, if still fresh when reaching Roncesvalles, maybe punch on to Espinal, (+6.5 km).