I don't think the number of words matter as much as that they sound distinctly different from one another and are no confusing or repetitive like lie down and sit down. The intonation should always the same. The biggest thing I try for are words that I instinctively remember and are easiest for me/you to remember. Twist and reverse (as many obedience classes teach) for left and right spins always makes my life harder. So I just use left and right.
That said it is possible to use some long sentences to convey a clear meaning. When I say excuse me my puppy has learned she gets a good girl!!!! if she leaves my big dog's tail alone. and let's go get a treat if I don't have one on me. Let's go get a treat is a sentence but it conveys a meaning and she's probably only cueing on my intonation and one or two words.
My requirement is that cues be clear and unique. I also do a lot of chaining b/c I do agility so I might have go, chute, right, come, hup, out, tunnel, go a-frame, come....YAY GOOD GIRL. So she hears a lot of thing a lot of short commands when she needs to be fast. But when she's driving me nuts with a ball and I say go lie down she will.