No, there is no rule that says you must have any monsters at all in your deck. You can make it 100% Spell and Trap cards if you wish.
Ritual monsters, and the rituals for them are in your regular deck.
Synchro Monsters are placed in the Extra Deck along with the Fusion Monsters at the beginning of a Duel.
You may have a total of 15 fusion and synchro monsters in your extra deck(renamed from fusion deck with the addition of synchro monsters)
A chaos deck is a deck that runs mainly light and darkness monsters where the light monsters are not lightsworn monsters. The focus of this deck is summon the chaos monsters(Black Luster Soldier-Envoy of the Beginning, Chaos Emperor Dragon-Envoy of the End, Chaos Sorcerer, and Dark magician of Chaos) while preparing to summon the chaos monsters this type of deck is also removing from play the opponent's monsters from play. This deck gets its name from not only from the monsters but also the booster pack in which this card were first released; Invasion of chaos. This deck works wonder with Dark Armed Dragon.
By adding Archana monsters that happens to be in Sortorius deck.
yes , you may place the monsters anywhere in your deck .
Approximately 20
Beast-Type support cards, since both "Ojama" and "Gladiator Beast" monsters have Beast monsters.
Destroyed or tributed Fusion Monsters go to the graveyard. They will return to the Extra Deck if something tries to return them to hand or deck.
A Lightsworn deck is a deck mostly consisting of the Lightsworn monsters, but with related cards like Judgment Dragon and Honest.
You cannot return fusion monsters to the hand. Fusion and synchro monsters have to be returned to the extra deck.
You can have up to 15 synchro's or fussion monsters total in your extra deck.