(Tako-Kichi. Re your multi-player flying, I've wanted for some years to explore the 'heritage' possibility of using old tech that is built-in to FS2002, FS2004 etc. to connect. You state 'SOH TeamSpeak 3 voice server.' I did join VATSIM years ago and got everything working, then didn't mess with it for a few years, then when I went back to explore, they'd changed ('improved'!!!) their environment and the old SquawkBox/TeamSpeak etc. was not longer supported and wouldn't work. I wasn't happy at all about that. Would anyone be interested to try an experiment to try a hookup via a single server, perhaps it only needs a shared IP address, per the FS2002, FS2004 original multi-player thingy? I just have this feeling that the old stuff will still work, and us philistines who don't want or need all the latest whizz-bang stuff are being short-changed by being advisied 'oh, that isn't possible anymore ...'. Maybe it is, we only need to try.)
The SOH TeamSpeak 3 server is a voice chat server that we use to communicate while flying online to save all the distractions of trying to 'type chat' in the chat box while fighting to hand fly an approach in bad WX like we did in FS2004 (although you can still type chat if you don't have a mic/headset). It can be set up for voice activation or PTT operation either via a button on a joystick or a keyboard key. It also has a built in file storage area so that people can share flight plans, textures, screenshots etc. among themselves.
We use JoinFS for our dedicated SOH multiplayer server since switching to the new Linux only server last year but unfortunately the latest version DOES NOT support FS2004/FS9 anymore, it only supports FSX, P3D, MSFS 2020/4 and X-Plane. When we had a Linux server and a Windows server we were able to run FSHost on the Windows server which was fully compatible with all the MS based flight sims and supported 'Hop Lists' which were very popular back in the day and SOH ran as many as 4 or 5 different ones concurrently (including a Round the World hop list with 970+ legs that took me many years to complete!)
FS2004/FS9 users would require some additional support to be able to fly with FSX/P3D users (the newer sims are an unknown factor) where a FSX user could act as a 'host' directly and others could join onto his 'box' or someone could run a private FSHost server and people from the older sims could connect to that.
HTH.