Discharge back-up sump above ground?
Pumping the water above ground, or below ground doesn't matter.  Moving the water far enough away (downhill) from the house is the key.  

If your plumbing is underground, it has to go somewhere. The pipe can't just come to an end. You'll want to drain into a dry well, ditch, storm sewer, spillway, stream, etc.

If your pumping out onto the ground. You'll want to be as far away, and as far downhill as practicable. 

In either case, you don't want to pump the water where it can just come back in or has nowhere to go.

A backup pump is always useful. Though if you're on municipal water, I'd recommend a water powered backup pump. Battery backup units are nice, but batteries tend to die at the most inopportune moments (Murphy's law).