Evolving 5* is a terrible idea early on, because of the max. level 60 needed for them. The XP and Gold you need to burn to bring a 5* from 50 -> 60 can easily be used to bring every member in the 30 to 40 range. And like Nikonana said, your 3* will most likely have 4 Slots and a high Skill Level that their potential Power can be raised further than what a 5* can get you, excluding the Event Girls.