I don't seem to find any GUI version which installs on current Linux and managed to install librePilot2Go Beta on an android 9 phone but it keeps warning it was designed for a previous version and may not work. The phone tells me it is version 0.3.2.1
It's my understanding that to get something running on a relatively recent Linux, you should use the latest next and follow the developer build instructions. 16.09 uses compilers from 5+ years ago and you should use a Linux from then. I personally have a Linux Mint box with Mint 17.2 on it that I use to build 16.09. I don't recognize the 0.3.2.1 number.
Here is a link to a development build guide ... oops looks like it is 5 years old:
https://librepilot.atlassian.net/wiki/spaces/LPDOC/pages/57671696/Linux+-+Building+and+PackagingI am pretty sure that the latest next will build on more recent distros than that. With latest next, I would recommend that you pick a distro that you like and try some distro releases say starting with 2020 and working back in time to find one that closely matches the build requirements. I started this myself in an effort to bring 16.09 up to compile on a recent distro, but that doesn't help you with building next. On a recent distro, next will be much easier to get building than 16.09
Getting it working will hopefully be a matter of mainly GCS and mainly what version of QT to use, and if you want to build in the GCS 3D PFD then you need OSG and OsgEarth.
I do not see any battery info but it seems to be at least half operational.
CC3D doesn't have a battery module. No room in the processor.
The firmware running in the FC and the GCS (LP2Go is a GCS in this case) need to match. Warnings about that should be stronger. You should assume that they MUST match. When they don't match, some things work and some things don't. The bigger the difference, the less things work. For Revo class FC's, the battery info must be enabled in System->Settings->HWSettings->OptionalModules. Press the red up arrow at the top to save it in the FC.
It connects and loaded a UAVO 16.09-086dc116. Does that tell me what firmware version in on the card?
Sorry. I haven't used LP2Go; didn't have a proper phone back then. The 16.09 sounds like ... 16.09. Other 6 to 8 digit numbers are usually either a git hash (tells exactly what source code was built) or a UAVO checksum (tells exactly what set of UAVOs = firmware setup is 100% compatible). I would guess that this is a UAVO checksum. If you could look for file dates of this file or files inside it might give a clue. On the other hand, LP2Go has not been updated in a long time and will probably not work with next without someone making a UAVO set for it. You might search the forum and wiki for LP2Go. I do recall someone discussing this, but any files won't be for the most recent next.
What firmware should I be running ?
I had a lot of toys set up with 16.09 that were working well when next was moving and changing. I didn't upgrade to next then. I still haven't.
For you for Linux, I would say that you should probably build and use the latest next which is 16.09+r796 as I recall (that means 796 sets of changed files since 16.09). Use whatever Linux you are most familiar with that can build this. I personally would choose a vintage of Linux Mint Mate.
How does this project relate to ClearFlight, which seems similarly stalled about 5 y ago 
CleanFlight is unrelated to LibrePilot. You might look here for some history:
https://quadmeup.com/a-brief-history-of-a-flight-controller-from-multiwii-to-betaflight-and-beyond/I would guess that ArduPilot is perhaps the most active codebase with good GCS and GPS support.