I just answered a similar question. Turns out I may have been lucky, one and a half days of rain. Once in Leon (we had finished walking) and once walking to Samos - it rained the whole day.
Really cold in Burgos and Leon, really hot everywhere else. Temperature was in the 20's (celcius) when we started - 43 degrees when we walked into Santiago. There was a big thermometer on the other side of the road from where we were staying, it didn't drop until well into the evening, the last few days were very hot in the afternoon.
I remember sitting outside a cafe in Melide about 5.00pm and watching the pilgrims walk in, and some of the new ones (the ones that joined at Sarria) were fried, bright red and actually blistered. Mainly I think because they started later and walked late into the afternoon, (having partied the night before?) therefore catching most of the really hot sun. I chose to walk earlier to avoid the heat of the afternoon.
So if you have fair skin I would advise earlier starts, sunscreen and a hat.
Also from Sarria onwards if you want some sleep, stopping either side of the bigger towns may be quieter. And the villages are cute. I loved Galicia. (I loved all of the Camino, but that part was really pretty, especially the mountains)
Galicia has the most spectacular lighting storms - you can see them coming. I was a bit worried carrying metal walking poles.