sounds like your thermastat is given up the ghost my freind.it might not be opening all the way causing the water to back up on itself.get it check first. ;)before you start panicing.
i never coast down hills.puts to much strain on the brakes and it dangerous,due to the fact there is no egine braking you run the risk of going into corners with little control.i would advise not doing it.
This tip will help you with milky headlights.What you will need is a sheet of 2000 grit wet and dry and cutting compound
Method-firstly Use wet and dry(wet) and sand your headlights,dont be affraid to use abit of elbow grease.
Secondly,apply cutting compound and polish headlights,do it a couple of times and you will have new lights.this works a treat.
regards.