Since Seattle 2072 has no Rules in it, it is fully compatible to to 5th ed. It lacks 3 years of History, but the city itself hasn't changed that much. Just a few Names might be different now.
The two big Rulebooks after Core are Run&Gun (Armor, Weapons, additional Combat stuff, Unit tactics, explosives) and Street Grimoire (Magic Sourcebook).
Then there is Stolen Souls, a Setting Book (New York or something like that? haven't read it), an update of what's going on in the World right now, a lot of Breaking and Entering and a few Rules and Items in it.
After that there were a few very little PDF's (~20 pages each): Gun Heaven 3 (about 30 Guns in it), Coyotes (about getting through the Borders of States), Assassins Primer (about Assassins, quite boring if you ask me), Bullets and Bandages (about healing people, haven't read it)...
and I think that's it.
I would definitely get Run&Gun, Street Grimoire has (if you look into the Threads on this Forum) a few problems and probably should only be bought if you have a Mage who wants every little inch of what's currently possible. And the rest seems absolutely optional. My group has most of them, but almost never uses them in any way. Even our groups "Full time, big grumpy Assassin" doesn't care much about Assassins Primer.