Just guessing but maybe shoot through umbrellas just to throw the light around the area and the softboxes of some sort on your models.

I am not sure. I only have speedlights for my setup. Another factor would be the lenses you want to use. f/1.4's and 1.8 gain you some ground on your lighting. Where Bobby Deal on this....lol.

This week I had great news :  the oldest city in Belgium gave me permission to shoot in one of their medieval churches in December.  And with "medieval" I really mean medieval - it's 700 years old!  This church has been deconsecrated lately (I had to use a dictionary for that word!), but the altar, confessional and pulpit are still there.
Anyway, I want to do a shoot with models there, but since it is such a beautiful church, I want the church to be fully visible in the photos, as a well lit background. 
Wedding shooters would of course say :  shoot wide open and cranck up your ISO, but we stock shooters know that is out of the question.  I 'd get refusals for "out of focus" and "noise".
So the only thing I can do is add lots of light.  The church has good electricity, so I can bring my 5 Elinchrom strobes and 2 Quadras, I could even rent more stuff.
My main problem is :  how can I get the most light out of my studio strobes, into the (dark) arches and side chapels?  And what light modifiers would be the best choice for such a great building? 
Any one with (lots of) experience in lighting larger spaces with very high ceilings?

I have the same problem... i plan a photo session (with models ) in a old church, Dome ( a out of use degraded one) i plan to use studio flashes and much of the natural light available. My advice is shoot in the middle of the day to get as much as possible the natural light.

Here are some pics with my location....
http://badorgood.com/foto/pierduta-in-negura-vremii-360789/396198

The roof and upper part was consolidated ... but the interior remain the same. i have only one day to shoot and no electrical power ( .... i must rely only on power packs.

1600ws is a lot more than I have, but my local dealer has Elinchrom 1200ws studio strobes for rent.   This weekend I'll be visiting the church for the first time (during an exhibition), so I can check out the color of the ceilings (and height). 

You say "high ISO"?  How high?  And was it for stock?

That sounds like a lot of photoshopping after the shoot, but it's not a bad idea to shoot the models with a tripod in the church, and then shoot the location from the same position, same settings, without the models, with a long exposure.  Worth trying ...

Thanks, that was a great idea, I immediately checked the few photos I have of the church, and I'm afraid I got a big disappointment now.  You see, it is not a chapel, it is a real early gothic church, and the lowest window starts at 3,5 or 4 meters above ground level, much higher than my highest light stand.
Of course, I could simulate your suggestion and put softboxes or umbrellas as high as I can in the line of the windows?

As for the theme: this is a unique chance that will not come again, so we will be doing several themes in 2 days, like gothic models, vintage religious themes and probably some halloween too (it's only in December, so we're still working on that).

Not a bad idea!  The panels that are used for exhibitions in the church will be left unused in December, so plenty of stuff to hang bed sheets on (or my lastolite vinyl floor stuff, which is more reflective).  Anything we can bounce on will be welcome, as the ceilings are too far away.  If I'm lucky, these panels are white by themselves and I can leave the bed sheets at home ...

For getting light on high walls or ceiling you will probably need the most 'light efficient' reflectors of Elinchrom. Those would be the HP 26cm 48�  reflector or the Maxi-Spot 29� 40cm.

If you can get hold of a studio power packs with a couple of heads, those would be the reflectors I would try. Best of luck with lighting such a light sink. Quadras will be fine for the models but wouldn't make much of an impression on the building interior.

I've no experience of this kind of thing so take this with a pinch of salt, but how about a large number of small slave flashes concealed throughout the building?

I've no experience of this kind of thing so take this with a pinch of salt, but how about a large number of small slave flashes concealed throughout the building?

They might work as some accent lights, but generally speaking they are just too weak. And also the recycling times are very long when used on full effect.

In this case I think you need all the flash power you can get, so rent some big ones from you Elinchrome dealer. Also I wouldn't light indirect or would use softboxes or umbrellas in this case, you loose way too much power and you need it all.
Personally I would go the wedding photographer way and would sell it through a macro agency but that is your decision. If you wanna shoot it with microstock in mind ( low iso and solid aperture) you need a lot of flash power!

Agree with the need for power. Pity that Elinchrom no longer produces the big 3500 Micro RF Power Packs that they used to. They sometimes turn up on eBay for a reasonable price with heads to match. As there's time to plan, it might be worthwhile picking them up on eBay if available and selling again when the work is done......a small amount of profit or loss could be involved because there is some demand for those more powerful packs still.
 Another approach would be to limit the amount of church you want as background and light accordingly (just a small part instead of the whole cavernous light sink!) All that's then required is a reasonably fast long telephoto lens to cut down on the expanse of background in the shot. Lighting could then be placed just outside the angle of lens view and close to the background wall requiring to be lit.

One last thought........rent some HMI daylight lamps for lighting the background. No worries about recycling times as they are continuous and an input of 1 Kilowatt produces the equivalent of 3.5KW of tungsten light but then at daylight Kelvin to match the flash. They may however be rather pricey to rent from a movie/film light rental agency.