I used to live in this area.
Driving is easy and roads are quiet.
There are frequent (and low cost) short ferries between: Kristiansand (N) - Hirtshals (D) Goteborg (S) - Frederikshavn (D) Varberg (S) - Grena (D)
In addition there are many smaller ferries connecting the various Swedish and Danish islands.
Longer ferries are from: Oslo (N) to Germany, Denmark Goteborg to Germany and UK Stockholm to Finland and Estonia
The new bridge is open and joins Malmo to Copenhagen.
Driving North from Frankfurt to Denmark is no fun! The Autobahns are very busy as far as Hamburg.
It is more pleasant to drive from Amsterdam. If you have the time Amsterdam/Hoorn/Groningen/Bremen/Denmark is interesting. Otherwise Amsterdam/Enschede/Osnabruck/Bremen/Denmark is faster.
Via Osnabruck you can expect to reach the Danish border in 4 - 6 hours depending on traffic.
It may be worth remembering that Scandinavian school holidays start early. Some of the more remote tourist areas start to close down mid August.
Peter Languedoc, France http://tlp.netfirms.com