1st option does not bring the app to the main screen just buried in the managed installed apps folder.
2nd option - a little confused here by what you mean. Somehow install google play and download kodi from there and it shows on the front page with the recent used apps?
3rd option - I think i've had this before but it doesn't add the app to the front page of the normal fire tv gui it uses its own launcher.
2nd option - download an amazon app store app (from some place like Aptoride - you need to adb install it to your fire stick)
This will replace the amazon app store app that the fire tv stick has so if you use it then it might not be worth doing this but it will show all user apps on the home screen
I don't think theres any other way to get apps onto the main screen other than these methods but if someone else knows feel free to say