dc chais

Getting someones heart up will not lower other characters heart. Although if you do not ship items that they like some of them will leave only returning when you ship the items. For example: if you don't ship enough fruits ronald may leave. The exceptions being basil who always leave for winter and remember that if they were always there they wont leave. Also not everyone that moves in will leave.

As for a "game day plan" don't do all activities in one day. Go fishing one day then the next go mining, then foraging and so on. Doing so you should come across everyone in town natural and when you see them give them a gift they love. Of course if you want to get married give him/her a gift everyday.