Is there an optimum way to level up characters?

Characters have growth stats, which determine how much raw stats each character gets when leveling up. It appears to me that the size of growth depends on how many stars the character currently sits at. So, the main question I have is: What is the optimal way to level up characters so that their stats and power is maximized?

Here are some related questions that have occurred to me on the question of optimization (the validity of these questions will depend on what the optimal path is):

1. Would it be optimal to max out a character's stars first, then level it up?
2. Or does leveling up a character and then later promoting it to a higher number of stars recoup the stats you missed out on the levels you've earned?
3. Does equipment come into play when determine the stats gained when a character levels up?
4. If there is an optimal leveling path, is there any way to correct a character's stats that was leveled up sub-optimally?