Stepping is a tell, in MMA, most only do it if they're going for a power hit, as the majority of kickers don't have the balance to recover afterwards. I would take a step only with the back leg and only if I wanted to do heavy damage.
The hand swinging is more of a preference thing, I keep my hands up, but I've been doing it so long that my hips snap into it the full amount anyway and I lose no power (relative to my swinging hand kick). The problem is that in MMA, they can catch your kick and make you eat a cross, which will result in you going to the ground, possibly unconciously. Now your hand up won't 100% stop this, but it will make your face less of a target, and you might just go to the ground feeling stupid instead of KO'd.