A duel coat is a coat that has a duel disk blade that is held like a guitar and is slung around the back when not in use. The duelist also doesn't need to draw a card as one gets ejected out...
The minimum number of cards you can have in a deck is 40, but you can have as many cards as you want beyond that. (Note that the Yu-Gi-Oh video games limit your deck to a max of 60 cards, however.)