I led a week tour of the Black Forest last May with a group of 13 bikes.
From the tunnel, we stayed the first night in Verdun at Hotel les Colombes, which is very cheap, clean and a bit shit. But has secure underground parking for the bikes, two boulangeries across the road where you get a French breakfast of a coffee and croissant for €2. It's also very close to the river, which has loads of bars and restaurants to choose from.
Second day was down to Villingen-Schwenningen-Schwenningen where we stayed for three nights at the Central Hotel, which is excellent and run by an Irish-German couple (Ronan & Jutta), so perfect English, secure parking, breakfast included. This is a really good base location as you do a few circuit routes in different directions. Some good Biergartens and other restaurants/bars in the town for the evening.
One route was over to Freiburg via the ski resorts for some amazing roads through the forest up to the mountain tops, then up to the Schauinsland cable car which is a lot of fun as mentioned above, then back across to Titisee and other lakes.
Another shorter day spending time doing a bit of culture at Hohenzollern castle, then on to Koblenz.
Last day from V-S, up the B500 - avoiding most of it to take nicer roads off to the side and then back again. Ending up in Sankt Ingbert to stay at the Alfa hotel there, which I highly recommend. Especially for the Monty-Pythonesque family that own and operate it.
Then up to Mons, stayed in the Van de Vale hotel there, which is a little pricey, but lovely for a last night - especially if you have friends in Mons to join you for dinner.
Then finally a short leg up to the tunnel and home again.
PM me if you want me to send you some proven GPX routes. We had an excellent time and I doing another trip there for 2023.
Thanks adm1. Your plan is very much up the same strasse as what we wish to do. I'll PM you shortly for GPX routes.