emmezeroline

KODI from network repositories does not have HW, so it will run slowly.
 
The S905X without HW can provide full-screen video at a resolution of no more than 720p. If you want to watch a full-screen video with a different resolution, either build and add components with HW yourself, or use Libreelec (it supports 4K video).
 
You need the correct DTB.

yes

To run Armbian, you need a new version of the universal multiload. You need to reactivate it using the latest Armbian images.

Can't comment on your specific hardware but see point 3. of https://forum.armbian.com/topic/2419-armbian-for-amlogic-s905-and-s905x-ver-544/?do=findComment&comment=58673
I have TWRP custom recovery on one of my tv boxes so I can issue the reboot update command from a shell in recovery.