No, face-down monsters are valid tributes, you are not forced to flip them first. There might be one or two cards that do require the tributes to be face up, but these will specify in the effect text.
No, a Tribute Summon follows the same position rules as a Normal Summon, so a monster you Tribute Summon is either face-up attack or Tribute Set into face-down defense.
If the attacking monster is switched into Defence position, the attack ends. Damage Calculation is not entered, you do not compare the monsters' ATK or DEF.
No. When a monster you control attacks a monster with a Defense higher then the Attack of your monster, you take damage equal to the difference but neither monster is destroyed. The only exception is due to card effects such as Des Kangaroo.
No not unless as a result of a monster effect, spell card or trap card.
You can tribute a special summoned monster, yes.
You cannot tribute summon a monster in face up defense position. You can either tribute summon a monster in face down defense or face up attack position. If you want to summon in face up defense, you need to special summon.
No, a Tribute Summon follows the same position rules as a Normal Summon, so a monster you Tribute Summon is either face-up attack or Tribute Set into face-down defense.
Taken from the Official English Rulebook: ...However, for Monsters that are Level 5 or higher, you must Tribute at least 1 monster you control before the Normal Summon. This is called a Tribute Summon. Monsters that are Level 5 or 6 require 1 Tribute and Monsters that are Level 7 or higher require 2 Tributes. Monsters that are Tributed are sent to the Graveyard and the "Tribute Monster" you are Summoning is played in face-up Attack position or face-down Defense position (a.k.a. a "Set").
If the attacking monster is switched into Defence position, the attack ends. Damage Calculation is not entered, you do not compare the monsters' ATK or DEF.
You can set the monster you tributed for, but the tributed monster is sent to the graveyard
No... a level 4 monster can be summoned without a tribute monster, but a level 5 and 6 needs 1 tribute monster and level 7 and so on needs 2 tribute monsters.
You put a monster in face down defense position BUT your not allowed to normel summon a monster in defense postion.
Torrential Tribute and Bottomless Trap Hole can only be used in response to a monster's summon. Attacking a monster does not summon it (note that if the monster is face down, this is a Flip and not a Flip Summon).
No. When a monster you control attacks a monster with a Defense higher then the Attack of your monster, you take damage equal to the difference but neither monster is destroyed. The only exception is due to card effects such as Des Kangaroo.
The core rules state that a Normal Summon places the monster in face-up Attack position, and a Set places it in face-down Defense position. Special Summons are face-up Attack or Defense position, unless stated otherwise. If the continuous Trap card 'Light of Intervention' is active, monsters can be Normal Summoned in face-up Defense position.
No not unless as a result of a monster effect, spell card or trap card.
You can tribute a special summoned monster, yes.