Thanks for the kind words!
The basis of the sandbox is that there can be multiple storylines going on at once, independently of one another. Each is divided into chapters that need to be done in order, but progress in one story will rarely be gated based on progress in another. Instead, you'll need to talk to the girls, experience key scenes by being in the right place at the right time, acquire items and resources, play mini-games, or upgrade the various projects.
For example, one of the planned key elements in progressing Melissa's storyline is building her a better office, which will require metal. To obtain that on the island, you'll need to upgrade the quarry to a proper mine.
If you really wanted to though, you could do it purely by trading logs and stone for metal at the docks, but that's going to be a pretty inefficient way of handling things - at least until I implement the tool shop so you can buy lumberjack upgrades, mining upgrades and the all-important Cornish Pasties!
I'm in two minds about whether to include a hint system. I think I'd prefer to handle it by talking to the girls and letting them give the hints.