No, credits can’t be moved from one account to another at the moment.
No, the device can only be viewed under one account where it was registered. The sharing feature will be implemented in the future.
Delete the device from your existing account and add it to the new one (just like a new device). Before deletion it is possible to choose whether to retain the measured data. The activation period of the device will not be affected.
Yes, the activation will be retained. Activation is bound to a given device for a given period of time regardless of how many times the device has been deleted and reinserted.