1) At the time Genovese crime family was the richest with the Gambinos creeping up on them.
2) the most dangerous family to be in was the Colombos. The most dangerous family to go up against were the Genovese crime family. I'll you why, when Costello and Genovese were housed at the same facility, they compared notes and realized that Tony Bender was playing both of them. When Strollo disappeared in 1962, there was finally peace and stability with the family acting as one overall when 1963 came around.
3) Lucchese crime family
4) Colombo crime family. The Bonanno family did not start running into problems until 1964 and by 1965 they started to come unhinged.
5) This is a tough one to answer. They were all mysterious to the public at the time. I would have to say Bonanno and Lucchese were contenders at the time, but Gambino crime family was a lot more mysterious and unknown to the public and LE. Take a look at those charts and you can see people were placed in the wrong family, Valachi, other informants and bugs helped LE to piece the families more accurately, but still thay got members wrong here and there.