Hitting on outside on fh is 'hooking' the ball. yes it's sidespin but you can also make square contact on the back of the ball coming across it for sidespin in the other direction like on the i/o. And you can also hit the top half of the ball on the outside. i do that sometimes on short balls and it really curves away a lot. and you can also hit the inside on a cc which i do just to mix up the spin in a longer rally. but the last 2 are advanced shots.
If I were you i'd concentrate on developing the up the back and across sidespin. That's the one used the most with this type of fh and it gives a little extra security and a nice kick on the bounce. It will also help you develop the angular momentum swing because to do it well you really have to be swinging on an arc.