The only rules constraints are that each individual Spirit must Grow / Gain Energy / Play Power Cards in that order, and that all Spirits must complete the Spirit Phase before anyone starts resolving Fast Powers. [p. 8] Other than that, players play simultaneously and may confer as they wish, so for instance, one Spirit could plan out their whole turn before another decides which Growth they're taking, or two Spirits gaining Power Cards could base their decisions on what to keep based on each others' draws. How lenient you are about individual Spirits rewinding - eg, going back to choose a different Growth option - is ultimately a playgroup decision, but most people seem to be fine with it so long as you're not rewinding "gain a Power Card".