The wealth of information that can be gathered from here is wonderful. All of you had excellent tips, links and ideas -thank you for this. I've begun looking into some of this already however no conclusions. Another pr Miss America photographer online recommended a Novotron V400D 3. I didn't realize initially that mobile could indicate out doors without electricity. As of the moment(but may in the future) I may have this need to shoot outdoors and did some reading about the key light and and fill lights. The mobile portrait studio (for now) will be for indoor use where electricity would be available and was planning on driving to the client's homes, doing a setup with a backdrop, etc. Granted, it is possible, they may want shots in their backyard or at a park but I have the option of calling the shots here and client will follow. So, to redefine for the moment, an indoor set up which would be expandable for outdoor would be a better description (my apologies for not being as descript as I should have been). I would think backdrops (black,white,green), Key and fill light, all white umbrellas or black/silver and 1 white, light stands and anything else to be added here would be helpful. Not sure of lighting wattage (?) needed for indoor (400 or 800 ?), I would presume 10x10 backdrops (?). Good ideas on the clamps and tape..setup is useless without those I would gather
I believe since the 5D doesn't offer a trigger, some type of triggering system is needed ? I did see the note on the Canon vs. the Knockoff. I do have access to a second 580 EX (not EX II). I saw a fellow photographer put both his 580 EX's on stands and bounce them off soft white umbrellas - that's all he had (2 umbrellas, stands and 2 x 580 EX's). Is this a good route for indoors to start (of course a backdrop is needed). lastly, I have a 7D that has wireless trigger built in - is there a way to sync this with the 5D MKIII or is this only wishful thinking on my part?
You can do very well indoors with a couple of 580ex II. These do not put out as much light as big studio strobes, but they put out enough for portraits of 1 or 2 people with modifiers like umbrellas. You can get f/8 at ISO 200 or f/11 ISO 400 with just 2 580Exs. If you like portraits at f/2.8 or f/4, then you have plenty of light.
You can certainly get started with 2 lights. In fact one light and a reflector for fill works just fine too. I mostly use 3 to 5 lights (all flashes), main, fill, hair or separation, and zero to 2 lights on the background. It all depends on what style of portraits you want to do. Actually, with white backgrounds 2 lights is not enough to blow the background out. I really need 4 lights on the background.
Shoot through umbrellas are the least expensive and most portable modifiers. A softbox gives you more control of where the light goes. When you are shooting in a home with light colored walls and ceilings, you will get reflected light bouncing off the walls and ceilings. This actually helps soften the light, but you also get a color cast from the walls and ceilings. You get more reflected light off walls and celings with umbrellas than you do with a softbox. This difference is small and if you shoot raw you can correct the color cast in post processing, so it is not a big deal. Most photo studios have dark colored walls and ceilings so they do not get reflected light.
For triggering off camera flash, the cheapest way to go is get a 30ft E-TTL cable from Flash Zebra or OCF Gear. This allows you to run a the cable from you 5D to one of the 580Ex that you can use as a master to control the other one. I have used this indoors and it works just fine with 580EX flashes on umbrellas. I also have PW+II radio triggers that I sometimes use indoors and always use outdoors.