it is very difficult to give a solution for your problems. Somebody has to look closer to your system and your environment parameters.
I have implemented the Decision Manager at a customer together with a Baan Consultant. I can say, that there are companies wich are using a data warehouse with more than one module (also in Germany). If you are interested, I can give you the contact data to the Baan Cosultant.
Feel free to contact me directly per e-mail (see my profile).