For the egg crate, you can stack them vertically or horizontally. I would not stack them very high, will reduce the chance of cricket escapes a little. How many depends on the amount of crickets, for 100, you could do 4 or 5.
If you're getting an adult, 100 should be fine. If you keep them they way Elizabeth does under her cricket guidelines, you shouldn't have a very big die off. You will have some loss during shipping.
You can freeze collards, make sure to let them dry out some before you stick them in a freezer bag. Cut or tear them into smaller pieces before you put them in the bag. You could individually wrap a small amount in foil or the plastic cling wrap before sticking them in the bag that way you can just pull out a serving to feed.
I buy large mealworms for my adult male and I would get 100 to start off with, unless you're going to order them, then I don't know what the minimum count is for the order.
I would feed them apart. Sometimes I spice it up by offering 1 roach and a few mealworms but it's rare that I do that, when I do it's usually roaches and a hornworm. Usually I just feed mealworms at one feeding and roaches at another.