Two things have mattered most for us when packing tile art for others to use.
Ship both forms. One sheet per functional group, which is what you already have, plus the individual PNGs in a folder. Some buyers drag a sheet into a tilemap editor and slice it there. Others want single files for an atlas packer. Offering both costs one export step and removes the most common support question.
Keep the grid exact. Same cell size everywhere, no stray padding on one sheet and not another, no trimmed transparent edges. Importers key on a fixed cell pitch, and a sheet that's off by a pixel is what makes a pack feel broken.
Put animated frames on their own sheet, since engines treat them differently from static tiles. And if you target a specific engine, include its own tileset resource file. That saves buyers more time than extra art does.