If you want to use NextPVR with Kodi, you should use the proper addon instead, no need for simple m3u and external EPG sources. kodi.wiki/view/Add-on:NextPVR_PVR_Client
If you want to host a generated file, you don’t need anything especial, you can use Dropbox and use the direct download URL
No, you can’t. This is due to the difficulty in supporting and adapting the .proto.gz or .tachibk format that Tachiyomi uses. Also Kotatsu and Tachiyomi and its forks have different data structures that they use. For Neko for MangaDex users we recommend to use Nekotatsu.
I have a box (X96 Max+), with a custom ROM, comes with only the essencial, but AndroidTV itself is not FOSS, the launcher and other services are proprietary, without it is just AOSP.
You can check the supported devices on the site slimboxtv.ru