I would get stuck into this idea with lots of variables. Each character would need a set of variables, health, attack, speed, dodge, luck etc etc which you would calculate together for each desired result.
PlayerAttack(2)*PlayerAttackSpeed(2)+PlayerAttackLuck(random(2)=5 - EnemyDodge(random(3))= 4 damage
I would set the timing of the turns by variables as well, but i believe there are timer objects and so on within Construct that would do the job.
I believe the hardest part of this would be making some sort of logic for what the characters will be doing with their turns.
If PlayerHealth less than 5 - Use Potion which has a value of (random(5)) etc
But just like the rest of this it would just come down to having the right amount of conditions for the game to choose from with random atributes to give a really dynamic result.