1) Forget all about your cable-receiver.. Just plug the antenna-cable into your DVB-C card and thats it! Decrypting channels with your providers smartcard is possible too. To encrypt NDS smartcard is difficult or impossible. But you have to be aware, not to break the providers rules!! And at least, there will not be any kind of support, breaking laws in this forum.. Just to have mentioned it..
2) there is a rotor-plugin for vdr that is capable to control the motor-dish. When all transponders have been saved to the channel.conf the dish will be moved to its position by vdr. I dont have a motor-dish, so i cannot give you details on how this works exactly, but old Google is your friend
...and yes, all the transponders/channels will be written to the same channels.conf
Hope it helps, and sry for my english too