We have several Trex surfaces on our playground at school. We have a Trex deck under and around our water pump table, in a covered playhouse, and on the flat decks and stairs of our climber.
I've never noticed that any of the surfaces get nearly as hot as the concrete sidewalks. The kids frequently go barefoot in warm weather and we haven't had a problem. Haven't had a mold problem so far, even on the water pump deck which is wet for long periods of time.
"A teacher who says, 'I am a good teacher,' is in trouble. A good teacher is frequently troubled, in doubt, frustrated. Perfection doesn't exist. Everyone needs help." (Amelia Gambetti)