Energy costs included in the price or charged separately: what's better?

This depends on how predictable consumption is in your property. With little variation, such as a short stay without air conditioning, sauna or charging point, incorporating a fixed amount in the price is the simplest choice. With large variation, because guests can significantly overshoot consumption, separate billing is fairer, since the economical guest doesn't then pay for the wasteful one. The implementation must be good though, because billing meter readings afterwards often leads to discussion; having guests pay upfront with live insight prevents that.