1. RPi4 supports hardware decode of 4K HEVC, but not 4K VP9, and not H264 (which is not a standard).
3. The TV should support a "Just scan" or auto mode. On a modern TV you should never need to calibrate the screen. And 1080p@60 is the best default resolution. Forcing the screen to run at 4K just adds load to the device. Kodi is already upscaling the 720p skin to 1080p, the TV will do a better job of scaling 1080p > 4K (native resolution of the panel) can Kodi does scaling 720p > 4k.
4. The filesystem is read-only apart from the persistent /storage area - this cannot be changed Anything you need to configure can normally be done in /storage, but we can't advise what to do unless you explain what you're trying to change.
5. Resolution determines the GUI (desktop) resolution. The whitelist determines the resolution/refresh rates to be used for playback if "adjust refresh rate to match video" is enabled. If the TV supports them, enable [email protected]/24/50/59.94/60 and [email protected]/24/25/29.95/30 (50/60 optional).
6. It generates more heat and draws more power, and IMHO is completely unnecessary unless you actually have 4K60 media. So far I've only seen test media in this format so I don't have it enabled.