>>915564>>915569I was in on a long-distance hike in Scotland this summer, so that will be down your alley.
Yes, since it rains a lot you absolutely need rain clothes, and unless you will not be active in the rain (which you will since I assume you want to be able to hike in the rain) you need those clothes to be breathable.
The jacket is the most important, and here I would recommend something that has a high water coloumn rating (at least 20,000 mm - see pic) Even though its breathable you can still get sweaty so pick a jacket with good ventilation - full front zipper, cuffs that can be adjusted and zippers for ventilation in the armpits are great too.
Even though all such jackets are advatised as water-"proof" expect to get wet underneath the shoulder straps and hip belt after hours of rain. That you just have to live with, and this is also why you need to be wearing wool or synthetic underneath
For pants a lighter shell would be best (more breathable, less water resistant), since they won't get the same water pressure as your jacket. If you can get a model with zippers all the way the legs its great, since you can take those on/off whithout removing your boots - this is also great for ventilation.
Lastly boots: I wore waxed full-leather boots whitout gore-tex. Normally I find this water proof enough for my /out/ use but if I was going on this trip again I would prefer some with a membrane. It just rained so much and sometimes for days without stopping.
Good luck OP