The €35 charge includes your line rental and broadband subscription. There are no download or upload limits with the service. Call charges are NOT included, so if you make outbound calls then you will be charged however much extra these total. It is possible to use the service on more than one PC, using appropriate router hardware - you should be able to use your router from Germany perfectly okay. Your monthly bill consists of an itemised listing of your calls.
Hope this answers your questions!
