Here is what I would suggest based on which characters have been known to co-operate together. The Joker would unbalance the team as he is Batman's arch enemy. Two-Face is only half villain. Mr Freeze is a loner and isn't a bad guy in the traditional sense anyway.
BANE is the kind of mastermind who would put such an operation together.
THE MAD HATTER for the technology aspect.
KILLER CROC is dumb muscle.
SCARECROW adds something different is has been known to be a team player.
THE PENGUIN adds brains and money and other resources, and he has been known to colaborate.
POISON IVY is the seductress andher powers over people and plants make her extremely, well, powerful.