The reason I don’t go straight for the bigger container for the whites and greys is so they are in close proximity to each other for breeding, while the populations are lower. The oranges are so active that this is not necessary for them. With whites and greys, grow them in the small containers for a month or two. When your population is visibly growing, it's time to move them to their bigger home.
Regardless of your container choice, don’t forget the air holes! I use a safety pin, heated with a candle or lighter, to push through the lid, melting your hole in. I have been using about 15 or 20 small holes in one end of the smaller containers and about 30 or 40 in one end of the bigger container. Putting them in one end may help allow the isopods a choice in hanging out on the wetter side or the drier side.
Substrate choices
I am having excellent results on ABG Mix mixed with 50 percent hand crushed leaf litter. We use oak leaves from our tree in the backyard. Any non toxic leaf litter will work but Magnolia may not be the best choice as we want it to be able to break down easily for the isopods to eat. ABG Mix is available from Josh’s Frogs.
ABG mix (4 quart)
You can find the recipe for it here if you want to make your own.
http://www.dendroboard.com/forum/parts-construction/63915-truth-about-abg-mix.html
ABG works well because it is light and airy, stays moist, and is packed with organics that your Isopods/Woodlice can eat.
A cheaper alternative would be a peat based mix with plenty of organics mixed in. Something like this.
2 parts Peat Moss (this is the pulverized, brown, dirt like stuff)
1 parts Orchid Bark (supplies wood for the woodlice)
1 part charcoal (I like the Cowboy or Frontier brand from Lowes because it is cheap. Throw some chunks in a pillowcase and smash them into about ¼ to ½ inch bits)
4 parts hand crushed leaf litter
It is a good idea to fully moisten, and then microwave your substrate, to kill off any potential bug eggs.
Your substrate should be kept moist, but not saturated, at all times. Isopods/Woodlice require humidity and humid air or they will quickly die.
I lay several pieces of brown, corrugated cardboard on top of the culture. I like to cover roughly 2/3 of the surface with the cardboard. Your cardboard will have to be replenished from time to time as it breaks down and is eaten.
Here is a shot of the type of oak leaves that has been working well for us. Also, a shot of a completed, producing culture, and just some Giant Oranges wondering where lunch is.