I agree it's a good idea to explore the swamp before fighting the Elder. Plenty of really useful stuff to find even if (and it really is extremely likely) you don't come across any iron.

But do NOT go to the swamp without poison resistance mead.

Mountains you should stay out of for now, because even if you make frost resistance mead the enemies in that biome will slaughter you in no time.

Sea serpents only spawn during the night and stormy weather, so Ocean is safe during clear days. The karve can also outrun the serpents when sailing at full speed.