@Urian:
Oda said that we are going to have one year of Impel Down and I believe that we are going to see the adventures of the Strawhats at the same time like the one that Luffy had in Amazon Lily only that shorter.
Nami, Usopp, Chopper and Brook are in small island where they can escape without fightning, they will learn something new for improving their habilities but we don´t see how, for example I can see Chopper learning a new ingredient for his Rumble Balls for making them more effective and less problematic than before.
Zoro could learn how to cut ethereal things. Remember that Kizaru said that Logia users aren´t heavy and Zoro needs to learn how to cut ethereal things, this will be very helpful against Logia users and and Pacifistas since Zoro could cut the internal energy of them with the new attack.
Sanji will become more stronger with his feets after running all the time.
Robin is the one who has the worst situation, with her handcuffs she is unable to do anything unless something special happens, but I doubt that in the bridge a powerful enemy can be found, they are all in Impel Down.
Returning to Luffy and the levels that he has to cross:
Level 2: Full of giant beast, the giant lion beast is here with giant spiders and things like this. They are very strong and the Lion Like creature is the guardian here.
Level 3: A Laberynth where the guardians are the minotaurs and people can be lost easily. Minotaurs are very strong here.
Level 4: Administrative level, this is where all the papers of Impel Down are done, prisioners are "death" here thanks to the power of Hannibal of transforming anything into gold. Prisioners are tempted here with an huge treasure and they become part of the treasure when they touch it.
At the end of this level an huge door can be found, level 4 and 5 are in the same height really. Crossing it will put Luffy and the others to the level 5.
Level 5: The real hell, this place is a giant swamp that makes the devil fruit users weaker than before and its population are centaurs who thanks to the waters can take any pirate with a bounty of 100 milions or more.
Luffy will know here that the rumored Level 6 is nothing more than a giant corridor that connects the top of Marijoea (where Ace is going to be executed) with Impel Down. Here we will learn that Impel Down was where Fishmen slaves where trapped and stored for their hard work until Fisher Tiger made his heroic act.
I was looking for smiley which bumps his head into something but couldnt find it…
Great chapter by the way and the most interesting experience for me was, how Oda has changed Buggy for me from annoying obstacle in the story progress to a cool side character…