A paper map is useful to have but should be used with care. They are all imprecise and it’s not possible to rely on them to estimate the distance between 2 places.
The same problems exists with google maps: the roads are too approximate to provide a good estimation of the distances between 2 towns (it systematically underestimate the distances). And since the roads on the map are not where they really are, the elevation data are also wrong.
We went there with a paper map which help to have an overview and ask questions. We also loaded the map from OpenStreetMap on the GPS and found it very very useful. Since OSM is a collaborative map, not all the roads appear but all those we took are there. The good thing is that if a road appears, it’s very accurate. By using the routing functions of the GPS we could get accurate distances between places. And it’s free!!!
You can use http://garmin.openstreetmap.nl/ to download a map for your garmin GPS.
You can view the whole route we took here: http://ridewithgps.com/trips/513818 (you can download the gpx file).
And here is the GPX: https://docs.google.com/file/d/0B-jhNkCWTDCGdlNUN09lcWZMYTg/edit?usp=sharing. It contains waypoints corresponding to all the guesthouses we went.