Digital is just like film, except ISO can be set from photo to photo and with something like a 5D Mk III detail will be a lot sharper. Shoot to raw files and you will have lots of dynamic range, or shoot to JPEG for ease of processing. In a controlled “Studio” environment you can avoid any need for the extra data in a raw file.
In theory, at least, you don’t need the Youngnuo trigger system. You can put a 580 in the hot shoe and set it to only pre-flash, to control the other flashes set to slave mode. Then you will be able to use Canon’s ETTL, or manual settings. This should work even if you are using softboxes since the light is bright enough to get through most of them. Using a radio trigger will let you get the light off the hot shoe, giving 5 lights you can move around, instead of 4. Possibly this is a bonus, or it just adds complexity. ETTL/TTL can also add complexity since the camera and flashes will work out settings amongst themselves, which can lead to undesirable results and no understanding of why the results are as they are. Start in manual mode, it will make your life easier. Start with one subject, that will also make your life easier. Get a plush toy or a used mannequin to use as a subject while you are setting up and working out distances and power settings, they will stay in the same exact position and wait patiently all day while you take test shots.
Since digital usually uses ISO values higher than film, you can use the 5D Mk III at ISO 400 or ISO 800 and still get quite clean photos. This will let you use less flash power from each unit, saving recharge time and battery life. ISO 160 or 200 will give the cleanest photos but you will need more light.
Start with one light, say camera left at 1/2 power, at about 45° to the subject. Take some test shots. Add a second light at camera right, at 1/8th power also at about 45° and the same distance with the same kind of modifier. Take more test shots. Add a third light from behind. Try out different power settings and distances. Add a fourth behind on the other side. Take more test shots. Vary distance/angle/height/power/modifier/etc., one thing at a time and take a test shot. Keep track of the change made and the effect. Do this with each light.
Indoors, pay attention to wall and ceiling colour, distance to walls and ceiling, paint reflectivity, and surface smoothness. In a small room with white walls and ceiling a single flash can light your subject pretty evenly from all directions because the light can bounce so much. Umbrellas spill a lot more light than softboxes. You can add grids to the face of a softbox to limit spill even more. You can put a grid on the flash to limit spill even more for dramatic hard shadows. You don’t say if you have stands and modifiers, or what those modifiers are, so this is all pretty general.
Light shining in all directions from a small source falls off at the square of the distance. Focused light falls off less fast. Light with a large modifier, close to your subject, will provide soft shadow and it falls off quickly. For larger groups, move the lights further back for less softness but more evenness.
There are lots of Youtube videos about lighting. Joe McNally’s books have lots of lighting diagrams with the resulting photos. He shoots Nikon and sometimes uses a lot of lights. All the concepts apply to Canon speedlites as well.
If you have specific questions, try to be as exact as possible, both about the space and all the equipment. Someone will try to give a reasonable answer.