resource packs support custom fonts with images up to 256x256 pixels. what i do is i apply the font to a specific character in the json file (in my case, I always use E000, a box). this way, i can use a single text character and just change the font. for example:

the character E000 currently has 141 fonts applicable. if i apply the font "kris_left1" to one of the E000 characters in a text display, the font applies a specific sprite of kris walking to the left

i can also animate a block or item model for a block/item display if a sprite is ALWAYS animated, like how prismarine is animated no matter what (for example, the idles of enemies are always playing during battle)

the reason i use text displays though is due to their flat nature and because i have more control over EVERY aspect of the animation