It would also be unproblematic to commission prefab wood house manufacturers with this: we also have a combo of waterproof concrete basement & wood frame prefab house (1.5 stories) on it. They do not build a waterproof concrete basement themselves, but have prefab basement manufacturers (usually the well-known national ones, Knecht, Glatthaar, etc.) as partners, but they can definitely plan & coordinate everything so that it fits. As long as you do not deviate from their standard partners, it is usually possible to agree that they also carry out the "basement" outfitting. Then you have more or less one point of contact. What you should not do is to tender the basement separately – most (wood) prefab house manufacturers find this rather difficult (if they even participate), and you will indeed have a lot of effort with coordination, scheduling, etc. However, in the end, of course, you pay the "order commission" somewhere (the large wood house manufacturers are, in my experience, somewhat more expensive, and possibly worse than the smaller, regional concrete plants). We decided on the "heavy" version, with corresponding extra effort in coordination on one hand, and price advantages on the other. Why do you insist on wood for the ground floor? Especially if the garage remains, I would definitely consider building everything out of concrete – this construction method is basically more expensive, but with sensible planning & corresponding construction schedule planning, it could be that you end up cheaper or at the same price. At least if you could imagine building with concrete prefabricated elements as a construction method. It naturally requires very precise planning (electrical, sanitary, etc.), as the revision possibilities are very limited.