I think you'll be fine if you use the beer PSI charts...
So, somewhere between 10-15PSI (at 40F) probably, depending how carbonated you want it. Most people set their Apfelwein at the same 12PSI they use for most beers...
I've never kegged Apfelwein or Hard-cider, but you should be fine at these pressures... I use the set and forget it method, so I keep it at the desired PSI at all times from kegging through serving the last drop. Works perfect if you have a leak-free, balanced system.
Roaring Bull Brewing Co.
Currently Consuming (HB): Apfelwein on Tap Troegs Hopback on Tap; Craft Bottles
Fermenting/Conditioning: Up Next: Hop Trio American Wheat, Lake Walk Pale Ale
In Planning Stage: Farmhouse Saison and Something Oaked.