There are some layers of complexity to this, and for people new to Zentyal (or anything else complex) taking it slow and methodically can help. I know that sometimes deployment time is against slow and methodical, but the benefits of that approach save time and reduce frustration in the long run.
Windows clients may or may not "see" Zentyal shares in the "network neighborhood" sense. That may not be a problem if Windows users don't need to see what's available because the shares are still available. Out of the box, Zentyal provides reliable file sharing despite the fact that network browsing is confusing. In other words, there shouldbe no need to edit configuration files for basic file sharing to work as expected.
Unless you have no access to a wireless access point (for when you add wireless), I think things will be more straighforward with Zentyal as a gateway. Just as a suggestion.