The database components are just to add switches so that it can be turned on/off from the admin side. If you don't want those, you can edit the code to ignore the switch settings and simply operate on a hard-coded configuration.
As for updates ... well ... until a grid-listing option gets built-in to the core, yes, you'll have to make sure you update your files whenever you update to a new version of Zen Cart. You don't have to wait for a new release of the mod if you are comfortable merging coding customizations manually. It all depends on your skill level and urgency of installation.
As for your "CSS/HTML" question ... the mod uses dynamically generated XHTML to produce the output, and hooks into existing stylesheet styles for displaying it. Feel free to adjust either as desired.
Bookmarks