weinstrasse

On your way to Freiburg from where?

Which Weinstrasse? There are different ones in different wine producing regions of Germany.
Which Freiburg? There is more than on Freiburg in Germany.

If you mean the Badische Weinstrasse, see the link here, then Freiburg-in-Breisgau is in the centre of the Weinstrasse and as good a place to stay as any. If not, then there are small hotels in many of the villages along the Weinstrasse.

Are you talkin about the Deutsche Weinstraße (on the west side of the broad upper Rhine valley in Rheinland-Pfaltz), or the Badische Weinstraße (further south, on the east side of the upper Rhine valley in Baden-Württemberg)? I assume you're not talking about the Frankische Weinstraße or the Sachsische Weinstraße, or the Bergstraße (on the other side of the Rhine from the Deutsche Weinstraße) that is also known for it's wine towns.

I will be driving from Cologne to Trier and plan to stay there overnight. Then I want to drive true weinstrasse( and probably stay overnight) toward Baden Baden.
My final destination is Freiburg-in-Breisgau.

That still doesn't narrow it down. The Badische Weinstraße is a continuation of the Hessian Bergstraße on the east side of the Rhine. The whole, combined route runs from Darmstadt via Heidelberg, Karlsruhe, Baden-Baden, and Freiburg im Breisgau to Basel. It roughly skims the western edge of the Odenwald and Black Forest mountain ranges.

On the other side of the Rhine (the side you're coming from), running roughly parallel, is the Deutsche Weinstraße. This runs along the eastern edge of the Pfälzerwald and Vosges mountain ranges from the towns of Bockenheim to Wissembourg in France.

Baden tends to specialize more in red wines, whereas Hessen and Rheinland-Pfaltz are more known for whites.

So... which Weinstraße is it?

And then if you continue south from Wissembourg, past Strasbourg, there is the Route des Vins d'Alsace, which is another Weinstrasse. This is parallel to the Badische Weinstrasse but on the opposite side of the Rhine Valley and is recommended.
East of the Black Forest you have the Württemberger Weinstrasse. You could spend many weeks doing all the Weinstrasse in Germany.

I think I am going to stay in Freiburg. So, the Badische Weinstrasse, seems to be the logical choice. I read, that I should visit Gengenbach, Durbach, Baden Baden... I am planning to spend 2 days for that. Do you think that's enough? Any recommendations?

Thanks a lot for your help!

The Kaiserstuhl is a wine area west of Freiburg in Breisgau. It is a hilly outcrop in the plain, separated from the rest of the Baden wine area. It has one town on the edge, Breisach, and many small villages. Staying in one of these villages would be nice. And, since you have a car, you can tour the rest. Click here for the official tourist site for Kaiserstuhl.

Look out for signs "Winzergenossenschaft". There are Winzergenossenschaft in the villages all along the Badische Weinstrasse, as well as in the Kaiserstuhl.
This is a village winery where the local farmers bring their grapes. They all sell directly to the public. You can go in and taste the wines, for free. When you decide which one you like the best, you are sort of morally obliged to buy at least one 6-bottle case of it. The local speciality is red wine called Spätburgunder (Pinot Noir in French). The more northerly wine areas of Germany produce mainly whites, but here they produce reds as well. Spätburgunder is very nice, but it is all drunk by the Germans, virtually none is exported.

Thank you very much for your advice Chris!

We love the Weinstraße and do it a couple of times per year. The most beautiful part starts just south of the A6 freeway (near Grünstadt) and stretches all the way down to the French border. But also make sure you do the little detour via Freinsheim, a small town still walled as if it was the 1500s.

What's the budget for accommodation?