Can I buy Hitman WOA PArt One and then buy all the remaining content later?

From other reddit threats, i know there exists the Upgrade Pack, but that seems like just 5 more maps while the Standart Edition WoA has few more and a freelancer mode. Is the linked upgrade pack the only think that you can buy after Part One? And if so, are you simply locked out of playing anything alse if you dont buy the whole standart edition?