Forgot one thing: that top bar is also entirely configurable. It's called waybar, and you can find the docs here: https://github.com/Alexays/Waybar/wiki/Configuration
Pretty much everything in Sway is configurable, as most of it is just written in a config file. You can use different application launchers (fuzzel, for example), you can add a notification centre like swaync, or just customise waybar with whatever modules you want. I think you can even switch out waybar for something else, but I haven't tried that myself.
Technically I'm sure it's possible, I've seen programs that have a kind of frosted see-through look. But that's something the program has to implement.