Looks like dissimilar metal corrosion in the presence of seawater. It's important to keep the engine bay dry and clean up any seawater spills (like from impeller changes or leaky hoses) thoroughly, so all salt residue is removed. Salt is hygroscopic and will attract moisture from the air above 75% relative humidity, so even if it looks dry you need to remove the salt crystals either by wiping or washing them off. Disused boats suffer from this more, as they're likely to sit around humid and unheated and spills may go unnoticed for a long time.
Definitely do clean up the electrical connections. You will likely find the cables to be green with copper corrosion and thus if the crimp connectors need replacing and not just cleaning up, the cables will too (or at least cleaning up the corrosion before re-crimping with a new shoe).
The engine mount function is related to the condition of the rubber inside, the corrosion is superficial and can be cleaned up, then treated with some rust converter paint and then painted over, if the rubber is still good that'll do the job.
As all of the corrosion is on the port side, check for leaks, although it may have been damage from an old leak. Give the area a thorough clean.
