as for keeping warm, it can be surprising how cold you can get riding in rain even at 20-25c or thereabouts. If there is wind, and your legs are all wet, you cool down, mind you this is coming from a skinny guy who gets cold easily.
A few years ago, a few of us planned a July trip here in Pennsylvania. We had about 5 hours of rain due to a stalled front. The temperature hovered around 68 degrees F or 20 degrees C. We got cold, really cold, while riding. Being totally unprepared for the amount of rain and the cool weather (the forecast had been sunny and 75/24), we begged a couple of large plastic trash bags from a restaurant where we had stopped to eat. We crafted rain ponchos by carefully tearing the bags to create a head hole and arm holes. These make a huge difference in helping to keep us warm. That made the ride much more pleasant. In fact, I keep a couple of trash bags in my panniers for just such emergency use.