When you fire Positron Blast your character staggers back slightly. Does this interrupt Standing Snipe? If so wouldn't this mean consecutive uses of this PA don't benefit from Standing Snipe unless you wait a second?

Yes, it does interrupt Stationary Fire, so a consecutive one would trigger Mobile Fire instead.

Hm, I'll have to do a normal attack in between each use to keep the ability active during the PA use. (A normal attack is enough time right? Any tips on this?)

It's not, but Stealth Shot with no crawl will take long enough to reactivate it.