1-Breeder boxes separate the mother from the rest of the tank so she can drop her fry and the other fish won't eat them. There are special slots that the fry drop through so that the mother can't eat them either.
2-I would take her out as soon as she finishes giving birth. Livebearers are notorious for eating their own young.
3-Yes, as will every other fish in the tank that is bigger than they are.
4-Ummm...not exactly sure, but I keep my tanks at between 78-80F and my platies breed like rabbits.
5-They do make fry foods, but I've heard that finely crushed tropical flake food works as well. I would consider putting live plants and java moss in the grow-out tank as they like to pick off that.
6-If you are doing a grow-out tank, I would do it bare bottom. That way you don't have to worry about misplacing any fry.
7-Yes, you can mix and match fry as long as they are the same size to start with. I have a guppy fry in with my three platy fry and they leave each other alone.
8-You can squeeze quite a few in, but remember that the more crowded they are, the more competition there is for food and the less they'll grow.
8-I would use a sponge filter similar to this:
http://www.petco.com/product/12147/P...:referralID=NA If you already have the air pump, you can get two of the filters at Petsmart for $7. I have one on one of my 10gal divided
betta fraternities and LOVE it.