Database imports

We have a few tasks ahead of us, with the first being automated updaters for :

Manufacturers
Categories
Category Attributes (new feature)
Products
Attributes

Do have any schema rules that we should follow to allow these to flow easily ?

Please clarify what schema rules you mean. Database tables?

We are importing product data en masse.
In doing so, we will be updating the support tables like manufacturers, attributes etc.

I wanted a list of dependant tables that have to be updated.
I hoped for a document rather than having to reverse engineer.

There's no developers documentation. I suggest to debug application while adding/editing products (\NopCommerceStore\Administration\Modules\ProductDetails.ascx.cs). It'll allow you to understand what tables are used. The same can be told about categories and manufacturers.