If the autostart.sh file is not there, simply create it.The Braswell N3050 should be more than capable of displaying 4K videos, albeit mostly upto 30fps. A Kodi gui running on 30fps is probably a bit laggy, but it shouldn't be that slow as you described it: "I can't navigate through a menu without some serious patience."
While running the Kodi GUI, give us the URL output of the following command:
every arrow i click trying to navigate it just hangs for up to ten seconds, and trying to go from the left of the settings menu to the right means 4 times the wait. I don't really care about 4k anyway, I just want it to run in 1080p :p.
As for the pastebin: SdRV