bus to Ranong is 6 hours, driving about 4< park at the market right near pier
Boat is 50 baht/seat or 500 for the whole boat ( they will wait for you to take you back. might ask for more if you dont speak thai.
you can stay up to 14 days but cant travel more than like 15 kms from town< theres a few hotels right near where boat drops you off as well as restaurants.,