is, am, were, was, are, be - the list is quite extenstive and depends on the sentence they are in.
Linking verbs connect a subject to a predicate adjective or predicate noun - they do not show action.
yes you are right about that
Well, the very last two lines state quite explicitly that the word <em>sepulchre </em>means grave:
<em>In her sepulchre there by the sea-
</em><em>In her tomb by the sounding sea. </em>
This seems a bit personal, can you explain what you need help on?