Heya! Affinity Publisher is the absolute bread and butter of doing rpg stuff in my opinion. But there's a cool integration between Publisher, Photo, and Designer if you have all three, where you can switch between them on the go in the same Publisher file. That said, Designer is probably the least necessary if the lot since Publisher comes with some vector editing functionality as it is.
So I would recommend at least Publisher, Publisher + Photo for all of the most important things (from my perspective), and all three if you wanna go all out!