You can change the directory.

You might want to look at distrochooser.de. That said, Linux Mint and OpenSUSE are good, stable distros.

I have found LibreX/LibreY to be quite good, as long as you use a stable instance

Here’s something you might find interesting “Why not matrix” Alternative onion url

Afaik yes but it’s not as convenient. (You’re sending a file, which the recipient downloads, instead of a video as a chat-item-thing). I’m not 100% sure on this though

Well the desktop gui is still in beta (literally less than a week old, iirc). So I wouldn’t expect it being on the website until it’s fully functional. (And it’s a GUI desktop client now)