How can I wire 7 outdoor posts correctly?
Since you are planning on using PVC conduit (this is different than PVC pipe) I would use thwn wire, (most thhn wire is dual rated as thwn or for use in a damp wet location).  You would run your conduit to each fixture and daisy chain all the fixtures. I have seen folks run 1 pipe up and 1 back down to make the wire pull easier but I just use a T and 1 pipe to each fixture both methods are legal I think a single pipe looks cleaner.