Regarding your points.
35.9). My tablet is actually the X605F. But I haven't added a SIM card to it. I don't need cellular data as I only use the tablet at home for light entertainment like browsing the web. Wi-Fi is enough for me.
35.10) Yes, it's possivle to install TWRP. In fact, I have done that when installing Ubuntu 20.04. But you don't really need it to install the OS.
35.11) There's no judgment of value when I say something is a problem. Every challenge entails a problem otherwise it would not be a challenge. There are few rough edges in UT, but the overall experience is quite positive and there's good support from the community. It's good to have an open mind and take UT as experimental for now. So, it sounds like you have a good approach to it.
35.15) Libertine is the point of entry to install Firefox and any app that is not distributed as a native app. The video teaches the basic steps of installing apps with Libertine. Another good source is the documentation. Unfortunately, the problem is that Libertine apps that require X11 (like Firefox) shows a black screen to me. The app is definitely running, but everything is black and I can even touch where the Firefox address bar would be to get a keyboard to show up. I have opened an issue with regards to this problem here. If you have any other suggestion please share with that thread. I am really eager to get this fixed as it will open a lot of possibilities for my use of UT.