I guess you are using the RC3 that came with the Nougat firmware, the final version will not appear as an upgrade, it did not appear for me. Also, unsubscribe from any beta testing. You could try to look for Kodi in the Play Store and see if an upgrade is available. If not, uninstall it and install Kodi 17 from the Play Store, but be aware that you will lose your settings. Second of all, Kodi is using the Wrapper, that is why that message appears when going back. I would recommend using the pause button on the remote instead when you actually want to pause the video. Pressing back will not pause the video, because when you are seeing the video you are actually seeing the Wrapper. I see you already unchecked the option for playing the next episode.
I cannot say anything about the delayed startup. Where are your videos? I have a Q10 Pro and I am using a HDD in it. I did not test USB playback or network playback.