Level 7 or higher monsters can only be tribute summoned by tributing 2 monsters, unless a card condition allows it such as Moisture Creature or Gilford The Lighting or the card condition requires it such as Victory Dragon. Yubel only needs two tributes.
Monsters of Lv5 or 6 need one tribute, and monsters of Lv7+ need two. So even monsters like Yubel (Lv10) only requires two tributes. Some high level monsters do require three tributes. These will always say so on their card.
Assuming the monster doesn't have any special text which explains how to summon it, then a 10 star monster just requires two tributes, because Lv7+ monsters need two. The Earthbound Immortals and Andro Sphinx/Sphinx Teleia are Lv10 monsters that are tribute summoned as normal with just two tributes.
You must tribute 2 monsters to summon one Flame Ogre.
As per the basic rulebook, you need two tributes for monsters of Lv7+. Some high level monsters have rules text to say they require three tributes, but these are exceptions. In the case of monsters like Yubel (Lv10) they still only require two tributes.
They are called Tributes
You need to tribute one monster for the tribute summon of a Lv5 or 6 monster, and two tributes for any that are Lv7 or higher, even Lv10 ones like Yubel. Additionally, some monsters require three tributes (Obelisk the Tormentor, for example), but that is stated on the card, and it not related to the level.
The Supremacy Sun is a Lv10 monster so requires 2 tributes.
Yes. Like Cyber Dragon, Gorz 'can' special summon himself with his effect, but he is not a 'special summon only' monster, he can be tribute summoned with two tributes, if you want.
Unless they are monsters that are special summon only, level 7+ monsters require 2 tributes.
Unless stated otherwise, tributes must be from amongst monsters you control. So you tribute the opponent's monsters for Lava Golem because he says so, but you could not for The Regulation of Tribe.
no
You need one tribute for a Lv5 or 6 monster, and two tributes for Lv7+, though many higher level monsters have additional or different requirements.