1.- You can select what files or directories to sync with wich device. But
fair enough I haven't use samba. As I thought it was meant to share with
windows and, fortunately we get cidmof windows in my house :)
2.- That depends on your configuration, you can backup everything.
3.- If you connect to a server with SSH and you want some file in your PC you
need to exit the SSH session and use scp command. Or open a different
terminal. You can't edit and save the file at once. (At least not that I
know, it might be possible and I just ignore how)
4.- Yes. Overall I wanted to give a simple easy to configure solution. I felt
like SSH was too much trouble for something simple. Not that SSH is bad, just
that Syncthing was maybe more according to Heather use case.