The line thickness can really play a strong role in how it will look.
There's nothing inherently wrong with a thicker line, but it does make things stand out more and that may or may not be the desired effect.

And yes - it can take a long time if you get going with deeper details.

Oh, NYC has various municipal buildings on islands, not just on the island of Manhattan.
Govenor's Island, Riker's Island [prison], I think N. Brother Island used to be a mental institute.. maybe..
There might be some others too, though I may be misunderstanding your statement.