I think that beginners should learn on single shots, as they are a safe action type, and stress the importance of making that first shot count. You can reload one pretty quick if you need to, so you are not totally limited to one shot, it will take a couple seconds to reload though.

Generally speaking, single shot rifles ballance well, are lighter to carry (no bolt or action to speak of), and can have longer barrels (2" or so) for their weight. Longer barrels mean better velocity for a given load.

The NEFs I have heard about are very good shooters. I have never picked one up. I did pick up a Mossberg single shot and liked the feel of it.
For the money I don't see how you could go wrong with a NEF.