Rapha, nice but a bit pricey?

For the top half, long sleeve merino base layer, long sleeve country jersey, pro team jacket with rain jacket for the rain. Debating whether I actually need to wear the country jersey or just go with a base layer underneath the PTJ. I'll probably pop on a winter collar aswell.

You will boil. Even in cold weather, the PTJ and the correct base layer should be adequate.

Do people even read the description for items and what they're made of and designed for, or just see "Pro Team" and think to wear it all?

Take overshoes, wind/rain jacket (or Windstopper gilet), base layer and a normal jersey. Standard bibs will be ok too. Normal fingerless gloves should be fine. 16-19c is really not cold at all. Cap under the helmet is advisable too, to keep the rain out of your eyes.