Hmm, been awhile since I dabbled with Ubuntu & it's like... Try installing Synaptic package manager to handle package installs and removal. Do check if your hardware is supported by Kodiubuntu, particularly the WiFi drivers. Kodiubuntu. Your system should be able to run Lubuntu, it being designed for lightweight systems. Have you tried the fuller Ubuntu on it? Either way, you can still install KODI as a program from the official KODI PPA.

Yeah, sure you can get KODI to auto-start in Ubuntu. You can configure other applications that should be started at login, in addition to the default startup applications configured on the system. For a smoother experience, during the initial Ubuntu installation setup, you'll be asked if you require entering the username & password upon login or being automatically logged on. Agree to the latter. If you already said yes, then you need to go to System Settings--->System--->User Accounts---><your_username> (something like that, pulled off memory) and make sure it's set to automatically log in.  Then with the help of the "gnome-tweak-tool" or "startup application"......See below;


Alternatively.... there's also Ubuntu Tweak and this.