You can use the same geas to cover multiple powers (but be aware that if you break that one, it basically means you're screwed because all your eggs are in one basket, so to speak). Some folks think it's safer to spread out different geasa over their powers, so that even on an off day, they can use some of their tricks. Really, which plan is "right" depends on your GM and how strictly they enforce a geas in the first place, how likely it is to come up as anything but a trivial inconvenience, etc, etc.