Any box or crate is ok - it just provides a safe, enclosed space for the hen and her chicks. I use cardboard boxes because I have a ready supply of them and I just throw them away when they get too dirty, but lots of people use plastic boxes which are easy to clean out and tend not to harbour mites etc.
'Mash' is any chicken feed (pellets or crumbles) that is mixed with water. My girls prefer mash over the dry food, although I always provide a bowl of dry food available 24/7 for them. It gets pecked at occasionally, whereas the mash disappears within an hour or two of me putting it out. Don't make too much mash at a time, as it goes off quickly. Some people throw away mash over 2 hours old, but I will leave a bowl out all day, then throw any remaining stuff away in the evening and start again the following day (and none of my girls have ever suffered for it!)
After the first egg hatches, the rest should follow within around 24 hours, and you should hear peeping a day or so before each egg hatches. If I have any that I think aren't peeping when most of the others have hatched, I water candle them. This means putting them in a jug of water at the same temperature as the egg - around 37 - 38°c (hotter or colder and you can shock the egg and kill the chick). Leave it alone for a minute or two, and watch if it moves. If you see a definite 'bob' then the chick is moving inside, and may need help to get out, as GitaBooks describes.
I am getting really excited for you - the countdown begins! Good luck.