It all depends, if there is a need to provide security between the CUCM clusters and hide the IPs then you can start using CUBE right away
If they're all going to be the same company and there is no need for hiding IPs for security then you can keep them with just GK.
You definitely need to include CUBE when you start using the SIP trunk, there was an ask the expert on SIP trunks that mentions all the reasons why the SIP trunk should not be directly between CUCM and the telco. But instead use the CUBE in between (Also outlined in CUCM SRND under trunks chapter). You might be interested on reading it.
interesting question! Im curious as well. If it was me, Id probably not "dual purpose" the gatekeeper. Its too important of a device to have (2) main functions on it. (SIP and gatekeeper funtions).
I have used gatekeepers in the past (in a pinch) as gatekeepers and MGCP gateways. I had some PRIs off the gatekeeper at a hub site and it worked fine.
I have not worked with the CUBE yet, but we would have to assume there is some sort of public/private in/out of this device to hide the identity of CUCM. With this, a security concern would be involved if you combine the gatekeeper and CUBE together. (which Im guess it is not possible anyways)
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...