Back before they started the series TFS made a cast list all the way to the Buu Saga not taking it seriously. This list would be thrown out later on. Many of the thrown out cast were of friends doing impressions while goofing around on Skype. Some were just put on the list in hope of deterring fans from asking if they could play said character.
The cast of Captain Ginyu was originally going to be Taka, but changed twice giving it to Antfish.
Taka has said in the a stream that if they had the chance they would change the main cast. Taka would be Piccolo and Kaiser would be Krillin. Lani got both of these role because he at the time had more experience and confidence in voicing them.
They have said they only pull cast from their circle of friends or people they know. This is to make sure they're able to get a hold of them if necessary.
The cast has been changed a few times. Some were because they lost contact with the VA (such as with KrisRix), other were creative differences (such as Vegeta3986), other were because of performance (such as lani becoming Master Roshi)
Because Shudo Ranmaru is voiced only as Panti. Android 18 is voiced by Amber Lee Connors.