Decker's equivalent to HyperCard's "backgrounds" is Contraptions; a Contraption instance can be the size of an entire card, if you like, or you could compose forms from several contraptions.
Duplicating template cards with deck.copy[] and deck.paste[] is also a valid approach. This might be desirable if you want to start with a template and then customize each instance beyond just the data they contain.
Another approach entirely would be to use a few Grid widgets to store tabular data in one place, instead of spreading it across many cards. See the CRUD demo for a simple example of this pattern. Storing data in grids makes it much easier to use Lil's query language to manipulate it.
Does any of that point you in the right direction?