p. 16 - It is written right in the front of the book that Luffy
says "10人がほしいな！” (I want 10 people) and next to it a bubble reads, "The ideal number of crew members is AT LEAST 10 people. The Strawhat crew currently has 9 people. Does that mean that at the very least we'll have one person join in the New World?" Many of the "secrets" are written out like this, meaning it's not actually definitive evidence, which is why it's hard to translate and find what's worth posting from this HUGE data book.
p. 17 - Talking about how Morgan became the way he did, evidently the one who tore him up and left him for dead was none other that Captain Kuro. He killed his whole crew and ripped Morgan's Jaw off. I'm not sure if that was known, but it looks like one of the "secrets" anyway.
p. 24 - What is the difference between Fishmen and Merpeople? Many Fishmen are short tempered and brutish and thus they use pure strength to rule over fish and sea monsters alike. Merpeople are much kinder and make friends with the fish, thus the fish try their best to help the Merpeople. (important or not, any info on Fishmen heading into Fishman Island is good I figure)
p. 25-45 - All the adventures of Coby and Helmeppo...Oda-sensei calls them...Cobymeppo...
p. 130 - Chapter 216 - After Vivi's speech, when they go back to rain base (crocodile's casino) you can see Mr. 3 standing out infront on the page where the people are saying Vivi's speech is 2 hrs late. He was obviously captured soon after...haha!
p. 312 - from chapter 524 it shows the big two page spread of all the marines gathered at marine ford. If you zoom WAAAAAAY in, standing behind one of the giants (black and white pin stripe pants) is none other that Captain T-Bone! The swordsman who Zoro tossed off the Sea Train enroute to Enies Lobby. (this is not important, I just had a good laugh at it).