If the God of the Bible is ALL-Powerful and ALL-Wise and ALL-Knowing, then it's very difficult to believe that He would NEED helpers to accomplish any task LESS difficult than creating everything which exists.
If He did not NEED helpers, it is difficult to believe He would have MADE helpers.
If He was ALL-Knowing, and KNEW that one of these helpers would become Satan, how could he NOT be ALL-Wise enough to know that creating Satan would be a PRETTY FU[c][k]ING STUPID thing to do.
So, no, I can't agree that there IS a "synagogue of Satan".
However, if ANYBODY on this Forum wants to drop me a brief explanation of WHY they think it was NOT a stupid idea for GOD to create Satan, please do so. Email through my R&S home page.
My guess is that this GOD does not exist, but the Tellers of Stories made up a story about Him, and, as any GOOD Teller of Stories will, they added stuff that would help the audience FEEL like the story was real.
Tribal chiefs had a few helpers, local kings had MANY helpers, and Great Kings (like PHARAOH) would have dozens.
So this SUPER -Being would have thousands. And, in any group THAT big, there's got to be some troublemakers.
PLUS: Without a BAD Guy, it's harder to interest people in the adventures of a GOOD Guy!
A certain skill as a Teller of Stories. Award-winning author.