Kart actually uses the SPR_* naming scheme as opposed to 2.2's SPR2_* naming scheme, meaning that, unfortunately, it is not possible to add extra frames of animation. At least not without any Lua.
As for tips, you could probably get away with making the ball an
Overlay. It's also recommended to look at
Kart's frame list to see how you should arrange the frames.
Oh also, good luck on making your character!