To determine if your deck is Modern legal, check if all the cards in your deck are from sets that are currently legal in the Modern format. You can use online resources like the official Modern banlist or deck-checking websites to verify the legality of your deck.
No, duel deck cards are not legal in the Modern format of Magic: The Gathering.
A minimum of 60 cards are required in a Magic deck for it to be legal in official tournaments.
Since August 2008, a legal Yu-Gi-Oh deck has 40 to 60 cards in the main deck. It is no longer legal to have an 80 card deck (cards in your Extra or Side Decks do not count towards your main deck size limit).
60
Yes
There is no standard rule of what is a legal cut of a deck of cards. Casinos each have their own rules. It is considered proper to cut near the center of the deck. If any player objects to the depth of the cut, as in only three or four cards being separated from the deck, then the cut should be repeated with a more centralized cut.
Trial by combat is not legal in modern legal systems. It was a practice used in medieval times to settle disputes, but it is no longer recognized as a legitimate form of legal resolution.
No, conspiracy cards are not legal in the Modern format of Magic: The Gathering.
No, they are not limited. You can have three of each in your deck.
A tournament legal 'cut' is one that divides a deck into two. Even taking one card is therefore a legal cut, it is the cutting into two that matters, not how many. That means cutting into three is not a valid 'cut' for tournament purposes.
You can find free online deck plans at different sites, such as www.deckplans.com or www.homeplans.com. You can also design your own deck plans at www.timbertech.com.
Zero. In case you didn't notice, THIS CARD CANNOT BE USED IN A DUEL.