How can a character take make more than 1 action in a turn? I think i have missed something, is it fatigue/stress or additional challange die on each addition action?

There's isn't an official way to take more than one action in a turn.

... I'm really not sure what penalty could apply to playing more than 1 action/card on your turn, I guess the convention is started by Channel Power and Curry Favour which add an additional challenge die to their actions if used on the same turn but they're not really the same as making two attacks in a single turn.

I think my gut reaction would be against trying it .

the card fakeout - if successfully can let you save up one conditional extra action and then ofcause there are the actual reaction cards ...