If the 11 spd Alfine uses the same cogs as the 3/7/8 spd Nexus/Alfine hubs, you can mount it with the teeth facing either inward or outward (makes more sense when you see it in person). This allows quite a bit of chainline adjustment. +2 on using the inner 39 tooth chainring and turning the outer into a guard, but there are lots of options, some requiring a shorter BB spindle, and yes, there are certainly single speed chainrings available. BTW, chainrings come in different bolt circle diameters, so they're not all interchangeable by number of bolts--measure your center to center bolt distance (in millimeters) between two adjacent bolt holes if it's not marked on the spider or chainring.
CC