I have used the poem Ozymanidas to try to show how the Iambic Pentameter can be used by a poet to emphasise and clarify ideas at the heart of a poem. I hope it is useful. Shakespeare Sonnets in year 7: updated might be useful in conjunction with this post, as might Sonnet 116 and Remember : Visualiser intros.
I would say line 6 also opens with a trochee.
The emphatic spondees are very notable too: “Two vast…”, “Half sunk…”, “…stretch far…”.
I think you’ll find this post of mine of interest: https://williamshakespeare.quora.com/Shakespeare-s-Rhythm-True-ease-in-writing-comes-from-art-not-chance-As-those-move-easiest-who-have-learn-d-to-da?ch=99&share=3a3ae916