If you're just shooting the flash difectly at the subjects then not much power is neededh. If you're using a soft box or umbrella (which I have to assume you're not since the flash it's self is more the you like to take), shooting at 100 ISO and f8+ then that might be stretching the limits of the little flash......and even if it does have enough power your recycle times will suck. If you're bouncing off a wall then the further away the wall is the more power you'll need (plus factor in desired ISO and aperture). Though since the head doesn't swivel that limits your bouncing options while on camera to basically the ceiling.
Correct, the umbrella stays at home. I will either shoot direct or bounce, or bounce + a white card for catch light (maybe get a flash bender or demb diffuser, but I'm not sure they are really useful). My settings... I usually shoot between f/2.8 and f/5.6, shutter speed would depend on how much ambient light I want to let in. I like environmental type of portrait, so I'm likely to use a slower shutter speed to get the background visible. ISO: I'm happy with anything from 100 to 400.
You're making a good point on bouncing off the wall. It's definitely going to require more power and I can't move the wall closer.

