Hiya and welcome to the community pal. Lucky for you our heroes forum is one of our more active ones at the moment so feel free to pop in there and get what yah need.
Have fun!
I've never seen warriors break out of their 15 character average mold but I'd love to be proven wrong since I love FE. I wonder how much of that amount will be DLC.
Warrior crossover games usually add half series characters and half original characters to the warrior title itself. We will see the protagonists, a few fan favorites, and new characters for the warriors title.
I don't know how they announced HW but I know that they only got to about 12-15 heroes just like every Warriors title. It'd be very odd for a warriors game to reach 30 heroes.