What should you be prepared for here?

You answered correctly. In rainy weather with poor visibility, you must expect a longer braking distance because wet roads reduce tyre grip, so stopping takes more time. Also, the visibility of your vehicle to others is lower, so you should drive more carefully and use your lights. Increased tyre traction is not correct here; wet surfaces actually decrease traction, making driving riskier. Always adjust speed and distance in such weather to stay safe.