What material is illegal and must be deleted?  Is there some place I
can go to get an informed decision on questionable material?  I am
seeking information on both illegal pictures and video as well as
illegal writings and music (if any).

Example 1: Child porn is illegal, but what about a mother posting
pictures of their nude child?
Example 2: Child molestation is illegal, but what about a fictional
story advocating child molestation?
Example 3: Bestiality (sex with animals) is illegal, but what about
life-life drawings or 3D renderings?

Who determines where the line is drawn, and how do we remain
uncensored and still protect ourselves and our site from fines or
prosecution?

If it matters, I and the web server are located in California.

This is a very complex matter, and I do not think it can be well
answered in the five or ten minutes that would usually be devoted to a
$2 question.

First child porn is a strick liability offense not protected under 1st
so just the fact of having child porn you will be prosecuted doesn't
matter where you received the stuff no protection Supreme courts has
found based on balancing test of the right of 1st vs children and in
this case children prevail

On hypo better to read up on 1st case vs virtual/computer gernerated
child porn their are cases do research

animals hopefully it's a s/l offense should be so should be virtual porn

Focus on where I can go to get an informed decision when necessary.

For $2?????????????

A tip. To tell how to convert a semiautomatic weapon to automatic is a
federal offense. This is not porn, but still illegal.