"Zero, one, or two?"

Yes.

You don't NEED poles, but they are so handy that I've always used them. As far as features, it/they need to be reliably non-collapsible, and sturdy enough not to break when you lean on them. Oh, yeah, and they shouldn't wear a blister on your hand. Beyond that, "features" are just a matter of preference and salesmanship.

My first pole was a wooden utility handle (walking staff) that I bought for about $5 at the hardware store. It was smooth, unvarnished, and never gave me any problems. It was long enough that I could plant it downhill easily to slow my descent and take some pounding off my knees. Eventually, I drilled a hole in it, near the top, to run a guy line through when I used it as a tarp support.

My next was a Tracks Sherlock metal staff, that used button locking mechanism. It worked as well as my utility handle, until the time I took a tumble on some moss-covered rock while crossing a stream; I landed with it awkwardly caught between two rocks, and it bent.

At that point, I switched to a pair of poles based on a friend's recommendation. Since then, I've tried a number of brands and models and, for no particular reason, find I mostly use a pair of MSR Overland Carbon poles (discontinued this year.) There are various locking mechanisms, and two-section or three-section poles, but I've never really found any particular disadvantage or advantage to any of them.

I guess, if I were to offer any advice on picking poles, it would be to find the grips that felt most comfortable in your hand, and get them - you'll easily adapt to any other features they have.