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.
Yes, the tributed monster does not have to be face-up at all, it can be tributed while face-down.
Yes. Face-down monsters can be tributed for tribute summons, card effects, etc.
Setting is similar, yet not identical to normal summoning. a normal summon is when you Summon a monster onto the field in face-up attack position, whereas a set is when you normal summon a monster in face-down defense position. When a monster is set, it is not yet considered a summoned monster.
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.
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.
Yes, the tributed monster does not have to be face-up at all, it can be tributed while face-down.
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).
Yes. Face-down monsters can be tributed for tribute summons, card effects, etc.
Tribute is only needed for the monster's Normal Summon or Set (or Special Summon in special cases). Flip Summoning does not require any tribute at all, regardless of what monster it is.
You can set the monster you tributed for, but the tributed monster is sent to the graveyard
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").
no the water monster must be face-up
Yes because it's effect says you can summon a normal dragon type monster from either players graveyard. So since tribute to the doom destroys the monster is effect activates.
Yes
Generally, no. Synchro Monsters are initially Special Summoned FACE-UP. Therefore, there is not a need for it to be Flip Summoned. However, that Synchro Monster may be affected by a card effect such as Book of Moon. In this case, the Synchro Monster is changed to face-down Defense Position. You can then Flip Summon it when possible.