Hello Steffen,
Thanks for the project. I carefully read your project description & I am able to handle this with my best care and professional manner. I have done this type of project previously.
I am sound knowledge in magento & I know how to upload configurable . Please send me the admin of the magento. 1st I am ready upload some product as sample. It helps you to check the quality of my work.
Please give me a message immediately to discuss the work! If you allow me, I am ready to start.
Thanks
Mostarik