Some LaTeX, but not all, especially for larger equations. I will admit it has gotten a lot better in recent updates, since it seemed thoroughly broken for quite a while in its early days.
I haven't seen video but it does have voice. And similarly I don't think it's screen-share, it's just editor state syncing, so live collaboration. Still quite a lot.
ST is a text editor while Zed is an IDE. I wish there were something like VSCode that is very modular but written in native. But VSCode is good enough and it is my daily driver.
No, that doesn't matter. I think you should be looking for how quickly it can get you a working environment for your favorite language not how long it takes to boot up once per reboot. If you want features the bits have to live somewhere. Look at it like a trade off, if you're just going to look at it, by all means, take a memory dump. But I find that a little bit hard to work with.
For me, as long as it's better than alternatives it's good enough. Especially if it's not running JS.
RAM does matter, especially when you have web browser with multiple tabs opened at the same time. Sublime Text or Notepad++ are powerful, yet much more lightweight than Zed. Not to mention Vim/Emacs.