I have no other DB to compare to neither, but I think you chose a good mix of motorway and small roads.
Only motorway cruising would be annoying after some time. What would maybe help keep the group together is to wait at given way-points (out of the little towns and city's) to form the convoy and continue the route.
When leaving SPA, I had quickly lost contact to the guys in front of me (bicycles and other cars) , and it took me 20 minutes to get back to the group.
There are also "national routes" in FRA, BEL and NED where you have 3 lanes (2 in one direction and 1 in the other, overtaking lane changing from side every 1-2 mls). These are easier for large convoy's.
All in all, something very similar to DB14 would be ace