There is no issue with using the same SSID and PWD for the 2 channels. If you use it this way you can take advantage of the 5ghz when you're local to the AP, but fall back to the 2.4Ghz when interference it too much.
However, in some cases, if your SSIDs are the same - you will have a wireless connectivity problem when you are connecting client that was 2.4Ghz adapter ONLY. (adapter gets confused).
Referring to the above I would recommend to use different SSIDs for the 2 channels (troubleshooting purposes too).