There's nothing legally stopping you from "selling" a copy of your store's database.
But you should really consider the fact that if you're going to push someone into using a certain piece of software which you have customized for specialty reasons, then you should be planning to provide the technical support for it too.
Example: if you're forcing a certain addon into a prepackaged Zen Cart site which you force your customer to use, then THEY won't have any clue that they're using NONSTANDARD software and that their problem might not be with "Zen Cart" at all, but rather with a certain addon ... and they won't have any idea that they need to mention that addon or specifically ask for help in relation to that addon. And then it takes the volunteers here numerous posts to drag the information out of them, and take them all the way back to square one of explaining what an addon is vs what is core Zen Cart functionality, before it's possible to even help them sort out their problem. And if their problem is something wrong in their hosting environment it may still be necessary to get them to install a fresh clean uncustomized copy of Zen Cart to specifically isolate cause/effect of a problem, etc. And it goes round and round.
And it ends up leaving them with a "first impression" of Zen Cart being complicated and maybe even unfriendly ..... all because they came in with certain expectations of "well, I'm using Zen Cart so all those volunteers at Zen Cart should know exactly what my problem is" ... when they're really using some hybrid which they can't even describe fully.
So, the short of this comment is: Be sure that YOU plan to offer FRONTLINE support to them, being their first point of contact for help with any problems they encounter, and for training them on how it all works together.
And be sure to teach them about PCI Compliance and their role in self-certifying all the addons you prepackaged in the bundle you sold them. Cuz technically they're responsible for everything after unzipping the official PA-DSS Certified Zen Cart release zip. And if you insulated them from that step then they need to be looking to you for complete details of all that you've done with it and auditing that you did it in a secure fashion. It would be fair for them to expect you to co-sign their PCI self-assessments.
Something to consider anyway.
The idea of an importable set of just products+categories from a CSV and a zip of image files ... becomes quite attractive when one considers the factors above.
You could help them set up the suggested addons and your custom template by providing some step-by-step documentation and tools to make it easy for them to set up and customize their own store to work well for your specific niche. And still offer support if they need it.