I am “buyer” of some weapon sets in marketplace, not creator.
Skeleton and bone animation for weapon is nice to have.
First person animations, would be also nice. There is first person default skeleton in unreal, use it.
Your biggest market will probably be single persons trying to make some indie game, so assume that total lack of skills in 3d modelling is common.
There are tools/plugins that allow editing such anims in unreal.
And some wishes from me:
make all your work consistent. for eg, if you orient meshes on o-x axis keep that for later works, or if you use grid that is multiples of 2,4,8,16 etc, keep that for whole assets pack, or bone names if you name some bone MUZZLE do not name another MUZZLE_FLASH
make versions of weapon for first person and 3rd person game
create sets of weapons, if you start with for eg. scifi keep doing them until you get whole set of scifi weapons. some creators make one asset for scifi another for pirate game yet another for medieval. It is very hard even buying multiple packs from multiple authors to gather consistent set of assets for same game, most look like patched Frankenstein game.