After some chat with the group and folks at Myrrys: Try 2.
Each character can take 5 points of strain without any problems. Each point above the 5 turns one of the normal dice to an edge die up to 7 strain. If a character has more than 7 strain, they are burnt and can not gain dice from backgrounds, concept or specialties.
Whenever a character witnesses something disturbing or uses a power, they gain a point of strain. This point can be removed with a successful roll (1 success is enough).
If the situation is risky, challenging or dangerous: the challenge die are rolled as in a normal roll. The price is a random trauma from the list of psychic trauma.