Tinkel Studios
Actually making a sandbox or a pure VN depends on the type of story you want to tell and the type of game you are interested in developing.
If you want to make some type of game that includes maintenance (evolve school, make investments, or anything similar), combat, or rpg mechanics, such as include side quests that can be done when the player deems (or can wait to do them to have statistics that allow it), surely a sandbox will facilitate your work.
If you want to tell a basically linear story, do a VN.