The main difference I'm aiming for is discovery. F-Droid is very focused on free/open-source Android software, while Stardust Store is meant to be a broader app marketplace with things like trending/new releases, rankings, categories, search, wishlists and download history. I'm still figuring out whether that difference is valuable enough, so feedback on that is useful.

F-Droid has discovery also, showing all new releases as well as the ones with the most downloads ('trending'). But it sounds like you want it to be more commercial, where you promote vendors who pay for it. Are users even looking for that sort of thing? To have even more apps be pushed on them than they already need in life?