Regarding which team to take in order not to change it or not to change it much.
I am doing every stage in every quest or map stage with two Delilahs. That is the backbone, that alone means three minions for every Hero almost at all times.
I make sure I take one Hero strong against Boss. If Boss and some mob are of the same element I take two Heroes of the strong colour.
Many Sand Empire mob waves will contain yellow enemies, there are also red ones so I am thinking this:
Delilah, Isarnia, Domitia, Azlar, Delilah.
This should be good all the way through all difficulties.
If you take some battle items like time stop for the last hard stages it is definitely sufficient.