I've noticed a slight problem.
It seems like I played the side quests out of order. I finished Sage's quest before completing Chanel's one. There is a whole section of Sage's quest (and of course Total Defence Party that appears once you finish it) that references the business opportunity that I am only now being offered as I finish the Chanel's quest.
I held off finishing Chanel's quest as it got a bit too grindy at one point so I spent some time on the other side quests. Then I got locked into the end sequence of Sage's quest.
My recommendation to anyone playing this is to play the side quests in order and leave Total Defence Party alone until you've finished Chanel's quest.