I had posted a book that was wishlisted. It was the only copy available at that time...the request timed out and now there are six copies in the system, including mine. Does this mean mine is number six or number one in FIFO, since technically mine was posted first but was held for a wish list?

I'm not sure but I think you would be #1.  Look at your bookshelf and see what date it shows that book was posted.  Is it when you originally posted it or the date the request timed out? 

You should be #1. 

I requested a book that had several copies in the system (5-10).  It timed out and in that time all those copies were ordered and it became WL.  It put me at #1 and then there's people after me.  Those people put it on WL while mine was still pending and it put me at #1 because I technically requested it first.  So I would think it would work the same way with books posted.

My guess is even if it put you at #6 it would probably get requested pretty quickly anyway.