I've already had something like this, I called it the "Ring Theory."
零, Rei/zero - zero/nothing/overflow: worn by the Akatsuki leader.
青龍 - せいりゅう, Seiryū - Green/blue Dragon - God of East and Spring: worn by Deidara.
白虎 - びゃっこ, Byakko - White Tiger - God of West and Autumn: worn by the unknown member.
朱雀 - すざく, Suzaku - Hōō (literally "Red Sparrow") - God of South and Summer: worn by Itachi.
玄武 - げんぶ, Genbu - Tortoise (literally "Mysterious Warrior") - God of North and Winter: worn by Zetsu. Zetsu's ring actually has the kanji 亥 (Kai, boar). The two kanji are somewhat similar in appearance though, which suggests an error by either the artist or the reader/translator.
空陳 - くうちん, Kūchin - The Void: formerly worn by Orochimaru and is still in his possession.
南斗 - なんじゅ, Nanju - Southern Star: worn by Kisame.
北斗 - ほくと, Hokuto - Northern Star: worn by Kakuzu.
三台 - さんたい, Santai - The Three Levels: worn by Hidan.
玉女 - ぎょくにょ, Gyokunyo - The Virgin: currently worn by Tobi, formerly worn
^---- Taken from Wikipedia.org.
They wear them like this:
Leader - Right Thumb
Deidara - Right Index
??? - Right Middle
Itachi - Right Ring
Zetsu - Right Pinky
Orochimaru - Left Pinky
Kisame - Left Ring
Kakuzu - Left Middle
Hidan - Left Index
Sasori/Tobi - Left Thumb
I believe that it does involve rank, so I support the theory. Deidara was only taken by surprise because it's not everyday you see a Sharingan user let alone the Mangekyou. That was a pretty unexpected thing, and I don't think he'd have prepared for that.
EDIT: From above me.
2. Kisame (The leader even said he was the strongest member)
No, that's wrong. He has the most chakra, not skill.