How much power

Still working on this, but was wondering for shooting on location shots of people, say eventually with either 5' or 7' octoboxes (will prolly get smaller one first) and generally will place a window with some light coming in to break up the background or add dimension, i.e. using the location as a location rather than trying to eliminate the background and turn it into more contained like in a studio.

How big a head should I start out with, I'd generally just allow for softer diffused light coming through anything in the background, yes this is a very broad option but please give me a place to start i.e. are something like the Elinchrome 400BX strong enough or the Profoto ComPact 300R or 600R going to do it, or not.

I want to work with the available light in many situations while using my initial strobe as the key and reflect the fill for starters. The intention would to use bokeh to smooth out the backgrounds but need to at least have some control options with the key light brightness. I just bought a new lens so the light kit will probably have to be built one light at a time.

Or will one of the Alien Bee's 800's work.

Elinchrom 400 should be enough. Get the biggest octobox you can fit, bigger is almost always better. Not sure using a window is a good plan, they reflect, and direct sunlight coming in at the wrong time is a pain in the butt.

Only thing to check is the power level of your strobe can go low enough that you can use a big soft box up close to the subject, ISO100, and the aperture you want. The 400 may be too powerful. The AB800 has a similar amount of power, from memory.

I'm fine on the window idea, not to worry and I've a lot of experience doing this shooting commercials so I won't get myself in trouble, just using it as a source for background depth but thanks.

I'm planning to go to a Profoto workshop here in a week so will ask a lot of questions. Something that's real important to me is portability and yet I want a solid set up with I agree-bigger is better with the octobox.

You say the Elinchrom 400 is too powerful, don't they have something like a 5 stop adjustment range which is digital so the color will stay good? and do they make scrims to reduce the light like on quartz lights? ones you just put on the front of the actual light?

Looking at Octoboxes, how big are they really, is a 53" octobox 53" across the front surface or is it measured across the back umbrella shaped part, I read on someones literature that it is the later.