It's pretty hard (impossible?) to sweep pick fingerstyle. In my opinion I wouldn't bother with sweep picking until you've got a good speed with both your legato and your alternate picking, especially the latter.
In my opinion, sweep picking is in no way necessary to play good melodic fast solos, they always just sound like showing off, so until you're pretty good with your fundamentals I wouldn't bother with it.
(just my humble opinion, I'm sure others feel the opposite)
Miracle Blade 4: Gibs on touch.