Hi All!
I used eBay live help to solve the problem, and I thought I would post it here in case anyone else has a similar problem.
The reason 'Seller Preferences' was not showing up in my Preferences was because I did not put a credit card and bank account on eBay. I had already put it on PayPal in order to receive payments, and I thought that was enough, but when you are a seller, I learned, you need to have this info on eBay as well!
Once I did that, amazingly, Seller Preferences showed up!!!!!!!!