Are silver coins able to be transferred between ships similar to gold coins using UPS strategies or are they only able to be transferred amongst ships with silver explorers.
Yes, they can be transferred with the Captain Jack Sparrow ability.
My understanding is one only needs a silver explorer to load silver treasure from a wild island after which the silver coin would be treated as normal treasure once aboard a ship. Is this correct?
Any ship capable of loading treasure can load silver coins, not just those with a silver explorer.
Silver coins are generally treated as normal treasure.
The +1 bonus only comes from the ship unloading the silver treasure at your home island, regardless of transfers and whether or not the ship that originally loaded the treasure had a silver explorer as well.