Correct, you can target as many creatures as satisfy the conditions. For reference, the relevant rules on spell targets are:
A typical spell requires you to pick one or more targets
to be affected by the spell’s magic. A spell’s description
tells you whether the spell targets creatures, objects, or a
point of origin for an area of effect (described below).
The spell's description tells us that targets are
Creatures of your choice that you can see within range and that can hear you [...]
The range of Compulsion is 30 feet, so you can target as many creatures as there are within 30 feet of you, provided that you can see them and they can hear you.
While gestures aren't part of the spell's magic, they might still be interpreted.
Before I start, the spell does explicitly say that the DM determines how the target behaves, so it's ultimately the DM's call. As I read it, gestures are not part of the magic of the spell, but they might be part of the mundane context of the command.
First, spells only do exactly what they say they do, and no more. If gestures were part of the magical command, they would have been included in the text of the spell. Specifically, the one-word limit reduces the spell's versatility--adding gestures basically bypasses that limitation.
Second, the spell only requires that you can see the target, not that the target can see you. If you try to use gestures to Command a creature that can't see you, does it still work? Nothing in the spell text says that the creature can somehow understand a gesture it can't see, because gestures are not part of the spell.
However, creatures have to use mundane, nonmagical context to interpret the command that they're given. For example, "approach" means that the creature has to locate you and figure out how they're going to move closer to you, and "drop" means the creature has to identify whatever they're holding and drop it.
If you issue the command "exit," and point, the creature may use the information you give it in order to carry out its command. However, they are not magically compelled to do anything other than strictly follow the single word command, so they might exit via other means, like teleporting away.
Best Answer
It is ambiguous, and may vary by DM and by situation.
The first line of command's spell description is
This implies that the caster must actually attempt to speak the command, and it must be expressed in a language that the target understands. Does whispering count as speaking? D&D 5E doesn't have explicit rules for language volume, so this will depend on DM interpretation.
However, command doesn't specify whether the command itself must be audible, or whether the target must be able to hear. And so this is a situation where D&D 5E is famously ambiguous and lets the DM adjudicate how the mechanics are resolved.
Suppose the the target is affected by silence but the caster remains outside its area of effect, allowing them to cast command. Assume the target and caster share the language of the command. The creature is deafened, which means they cannot hear, but the deafened condition doesn't specify anything about understanding language in general. The caster speaks the command aloud, thus the spell requirements have been met, but the target cannot physically hear.
Would this count as speaking to the creature? Can the deafened creature understand the language of the command spoken by the caster? The rules don't specify this, and so the DM decides.