The cosmic-greeter package is already installable today. It will work on any system that has greetd available. The Appearance panel in COSMIC Settings is not yet merged, but it is in the appearance staging branch.

Tbh, cosmic-epoch itself is kinda modular, yet slightly weird. I used it on nixos for a short while (until some shit in nix changed, and pop's flakes decided to not compile) recently.

The strangest thing is their way to store configuration: cosmic-comp (I.e. their compositor) has 2. The 1st is a "regular" file (.ron, as far as I remember) and is used to store keybindings and some other settings (for example whether to tile windows automatically, border width, etc), and the second one is like windows's registry on top of the filesystem (I.e. you have ~/.config/cosmic/com.system76.whatever/dir0/file0 where dir0 represents some group of parameters (?) and file0 is the name of one; the value is the contents of file0. Easily manageable with nix but confusing AF to edit manually. Most if not all except the compositor uses the latter format.

On the other hand, the compositor is already quite cool with regards to animations and window/workpace movement at least, and is reasonably stable for a pre-alpha. Also, their way to make bars seems interesting: each applet itself is a graphical app using xdg-shell, and the panel uses pop's lib to "convert" them to layer-shell.