InvisibleMan

If you take the original Gaiden town exploration / MyCastle 2d style and make it 3D like the SoV Dungeons that could give a natural way to incorporate some free roam into the game, but it would be kinda reliant on a World Map system. You'd have towns on the world map you could enter to shop / do quests / progress story and between towns (or perhaps on newly discovered ones) you would have combat.

Well Hyrule Warriors (Legends) has 25 characters in the base game and an additional 4 as dlc. Given that it is a conglomerate of the original wiiU version and all dlc (if im not mistaken) and using it as a benchmark for Fire Emblem Warriors, I would estimate probably around 20 characters in the base game and up to an additional 10 of dlc. Probably prioritizing ShadowDragon, Awakening, Fates, in the starting roster, with Alm and Celica additionally since they're getting a remake, and three sets of dlc containing the major characters from other games (Genealogy set, Radiant set, Blazing Set). Guaranteed Anna the merchant.

Honestly, It is a matter of taste. I personally haven't played a warriors game myself, but I find the concept of single-handedly plowing through hundreds of enemy units quite invigorating. I suppose it might get old fast, but a fairly sized roster of different characters with unique playstyles might remedy that situation. I don't think it would necessarily be a big hit with most of the fire emblem fanbase as hack and slash is basically as far as you can get from strategy oriented gameplay, but I imagine many people will get it just for the characters and for the sake of supporting the franchise.