I cast Force away targeting my only creature who's a vanilla 4/4.

As Force Away resolve, should I draw then discard ?

No, you should not.

As Force Away resolves, you follow its instructions in order, so you will return your creature to its owner's hand before checking the Ferocious condition to see if you can draw. If you don't control any other 4+-power creatures, the condition won't be true, so you can't draw.

Daniel Kitachewsky
L4, Paris, France
Rules NetRep