You can choose the port you want for data-link.
For control-link, you can only use the dedicated port on the SFB. It's an SFP port, so you can use fiber or copper, depending on what SFP you have.
For dual control-link, you need 2 RE's per chassis. This is way overpriced since a second RE in this chassis only serves for this purpose (no RE redundancy yet)
The doc states that in case of control-link failure, the chassis tries to use the data-link for control messages to minimize the chance to go in split-brain mode.