So the gift ranges are as follows, along with points they give on challenge mode (assume that each value is doubled for easy mode)
This list is still not entirely comprehensive but it details all you really need to know about what you need to gift each girl!
All girls usually have 2 preferred items except for the two princesses who only have 1!
You can assume that everyone likes all of Serena’s luxury shop items but each girl has 2 luxury items that they’re only okay with
Remember that repeatedly giving the same item to a girl usually has diminishing returns on love points (usually half of the usual), so you need as much variety as you can, especially on challenge mode!