Gnome isn't a distro, it's desktop environment.
Each distro is different and the most important thing you can learn for a new distro is the package manager. Most any distro is gonna say, always use the package manager as it is best practice. This doesn't say you can't install via source, but all headaches of installing, running, and maintaining that package is up to you.
Here, all you have to do is go to our bugzilla page, request a new package, give the information the DHalens posted and the entropy team will look at your request for the package.
If you feel brave
emerge --sync && layman -a keruspe << you are adding the overlay to get the package, much like adding a repo in ubuntu
emerge -pv kupfer << you do this to see if it will pull many other files and if it does, use equo to install whatever packages you can, hopefully most of em
so lets say you do emerge -pv kupfer and it was to pull 3 packages foo1, foo2 and foo3, check equo
equo install foo1 foo2 foo3
the worst it will do is say nope, we don't have it sorry, hopefully it has them and it installs them, otherwise continue with the