I don't think this is a difficult trip at all from the planning point of view. I looked at the route and one thing I noticed was a slight lack of VORs, but the OP said he was interested in doing navaid tracking. Of course with a GPS it is easy and there are plenty of airways intersections which one can use as ready-made GPS waypoints (any half decent GPS will have these in its database).
One can do the route generally avoiding high ground, too, but flying on a hot summer day underneath the small white fluffy stuff (you can tell I never did the JAA ATPL ground school, but I do have the chart showing the 371 different cloud types on the wall in the downstairs loo) can be awfully rough, and one may well choose to fly above the layer, so I would plan the route where one can fly at say FL065.
Weather is the big issue, as stated above. A large high pressure area would help a lot (I flew UK to S. Spain in one of those in that amazing summer of 2003) but what is the chance of getting one over Newcastle?
Maybe he will get lucky... One needs to sort this out with any passengers; if they "must" be back at work by a certain date then you can have a major issue. I have only narrowly avoided having to buy airline tickets for people in the past. In this case, the passenger being an instructor should be ok because he must know about this angle.
The route planning and the flying itself will be easy
As always, phone the destination before departing. In this case, the area is subject to rapid and unforecast fog formation so checking is vital.