This game is more focused on the girls/their romances and stories rather than the adventurer parts. The adventuring is more secondary than anything.
As for Slaves, there probably won't be any extra slaves added to the story, but players will be able to choose slave routes for some girls.
And Bront and the Goddess are important to the story, and will have a lot of content, but their stories will be after act 3/4.
Currently I'm in act 2 right now.