Does Reflections gain the power and energy costs of the chosen unit?

Yes, a Reflection unit token does gain the energy and power costs of the unit it is copying.

According to RiftJudge FAQ #8759, cost is an inherent trait that is copied when a game object becomes a copy of another. While tokens normally have a cost of 0, when a token becomes a copy of a card, it adopts all of that card's copyable traits, including its base energy and power costs.