
To unlock the New Game+, where you can play on a new island as your child with all of your money and Makers, you'll need: 1) Collect all 5 rainbows 2) Reawaken the Harvest Goddess 3) Give the Journey Rucksack to your child.
Give villagers many undesirable gifts and you'll get unlimited chances to give them better ones -- their affection will stop at zero, so don't worry about negative numbers. It may be tedious, but giving hundreds of desirable gifts is an easy way to raise heart levels.
Request a Rucksack Upgrade from Shelley without the needed materials and Shelley will still gain heart points. You can do this indefinitely. This can make moneymaking easier in the Tailor Shop.