Have done trips around Europe in the past with a relatively light bag. Had my K-50 back then and took with me the following lenses :
18-135 for walkaround
55-300 just in case I needed a telephoto
DA 15mm for landscape shots
DA 35mm f2.4 for indoor and low light shots
80% of my shots were with the 18-135, the other 15% with the DA15mm. The rest were with the DA35mm and 55-300.
You definitely need WR because in England/Scotland it will be raining a lot.
If I were to do it again with my current lineup, I would only take the 18-135 and DA15mm. My 17-50 f2.8 might come in useful for indoor shots, but isnt exactly light. Would probably end up taking that as well and hardly using it
Trust me, you will need a light bag. Your shoulders with thank you