I'm starting my new project, a 6 foot vinyl privacy fence. a lot of
online resources recommend putting gravel into the holes (6 inches
worth). Is this really necessary? i figured with a wood fence it would
be to prevent rotting. But was wondering if placing them directly in
the concrete was bad... seeing as how they're vinyl. i'm in norfolk,
va. if climate is a factor.

I don't plan on putting 4x4s down the center of the posts, only at the
gate.

also, any tips? I was planning on putting the corners in first, then
tying a string corner to corner - then staking out where the posts
should go. I was going to do dig all the holes, but do 2 posts/panel
at a time to reduce the risk of error. (instead of all the posts at
once, which i'm sure i'd screw up).

Thanks for the help everyone!