Yes, the CI0 can typically power and control one mini-camera on each port. The CI0 is not meant to power larger camcorders that typically run on batteries or supply and in this case the control cable will not include power. For some camcorders like Sony ENG cameras, the CI0 will be powered from the camera in which case power doesn't have to be provided by PoE or external (the right cable is necessary for this). You can find more information on power here in the CI0 Manual.
There's no limitation. You can use as much CI0 as needed.
Only one RCP can control a CI0 and the camera(s) connected on it. The pairing happens once the CI0 is used in the configuration of any of the RCP in which case it becomes unavailable to the other RCPs until removed from the configuration. If one camera has to be controlled from multiple RCPs, we have multi-operator workflows using the CY-GWY or upcoming options using a distributed architecture for remote production.
The RCP, GWY and RIO can be configured with multiple IP addresses and the default route for internet access can be changed as from releases 21. Typically multiple IPs are useful to reach a range of IP cameras (typically PTZ), a technical network, change the internet access from DHCP to static or add special routes for VPNs or vlans. See IP Configuration. You can't remove the factory IP though as it is used to control devices on the local network like a CI0. The CI0 IP can't be changed at this stage, we have plans to allow that in the future but in all cases a CI0 is not the right device to go over latency networks such as VPNs. A RIO is typically used in these cases.
The GPIO-8 is an active cable with electronic components and IDs for auto-detection.
Yes, all protocols we support can be mixed on a single controller, even the CI0 can use different protocols on each port.
Yes, the easiest way is to connect an LED to the 12V output of the second port. There are some other pins that can be used for GPIO and which could drive external electronics to control a tally light.