Nick is allowed to know exactly what farmhouse is meant by the farmhouse - though of course merely dropping on in to see the one calling it base would not be unquestioned - and it is indeed within the Echo boundary!
And on your second question, there would be absolutely nothing to stop Nick from making a list of officers who he identifies as not-quite human.

Lastly, by the Sheriff we do indeed mean Edwards - with apologies for the terminological mix-up!