We buy most of our studio supplies from
CalumetTheir online info is good, and it's well worth ordering one of their catalogs as a reference. When you call, you usually find someone who really knows what they are talking about.
Lot of info on portable backgrounds there, too. We use some "pop-up" versions, I believe from Photoflex, but usually find them too small exept for seated portraits. We also have some nifty Bogen stands with crossbars that allow us to drape backdrops up to 20' wide, but can be used smaller with shorter crossbars. You could even get by with several large "clothespin" style squeeze clamps from a hardware store for draping backgrounds where there is anything to clamp to. I don't remember the name, but Calumet also has some collapsible backdrop frames made from hinged PVC pipe, which we also find useful for suspending large diffusers in front of lights or windows, or to cover with large reflectors. They're not bad as large scrims when you want to control light spill.
As for what's the minimum light power and number, a WHOLE LOT depends upon the effect you want to create. On location we sometimes can get by using a single light and reflector, where ambient light and backgrounds are suitable. As Bob says, two lights is about minimum when you want to completely control the light, and four is better. I agree that 800 w/s is about right for most uses. We have them as small as 250 and as large as 4800, but most of our unilights and powerpack lights live their lives between 400 and 800 unless venues or sets get large. The most-used shooting room in our studio is 14x30, and for that a 4-light set with the key light at 800 is almost overkill.
