Hi Val
I am pleased you have chosen "Walking The Ahr Valley", This is a great little trip for your first holiday experience with Just You, I can confirm that you will enjoy it immensley. It is set in a beautiful town in a great location, With fantastic views , As for the walking it is not overly difficult and you do not need to be a season hiker or walker to conquer this. Although a little training as you said will not do you any harm. The Red Wine Trail which is the longest of the routes, Is on relatively good tracks and some roads. Although there are a couple of small goat type tracks to endure. My advice however is to make sure you take some water proofs, And some walking trousers. As you could encounter a mixture of weather from very hot sun, To rain all on the same day. Some of the route is open as you walk through the vine yards.
Have a good trip
Andy