Easy "Abuse no more" Achievement
Witness Lee and Matilda 2nd event in their house with a high friendship score with Matilda.
Easy "Saw your abuse" Achievement
Witness Lee and Matilda first event going near their house past 9pm.
Various Gameplay Tips
It can be useful to focus on upgrading your farming skills and fight monsters and getting farming related perks and drops from monsters to sell before you head over to the mine. And don't be afraid to save some crops you grow to get stamina back so you can get a larger harvest next time around.
In combat, it is much more efficient to "charge" your tool (ie hold the attack button) then release when the enemy is in position to be hit, instead of just tapping the attack button. Some enemies can be quite dodgy and that's on purpose.
Treasures. Westend of the map near the lake. On the roof of the hospital.
Community Projects reward/secrets
Pier: You can get a full armor set on the other pier
There is a hidden cave behind the waterfall you can sail into, there will be a chest with ~4k gold and some speed boots.
Well: You can find Dennys sword, after gifting it to him you will be rewarded with a shadow plum that increases stamina.