I have learned that the guys (girls) at the paint supply store are there to sell paint. Whether you need it or not.
And..... more times than not, they have no idea how most of the products that the sale work.
You should be ok to just leave off the etch and apply the Sure Seal to the bare metal.
Here's a hint: You are going to need to seal your work before you apply your top coats. If you get some Epoxy Primer, you can reduce it and it makes a perfect SEALER.
So you can always use some Epoxy Primer around the shop.