Hi,
Yes, you can add it directly to the database. It has to be done in the falang_content table (or joomfish_content if you use JoomFish).
Regarding the categories assignation, I suppose that you're talking about doing that with the CSV.
You have several ways to do that.
If the categories are already in the database, you can use the id of the category instead of the name to easily differentiate them.
Otherwise, you can use the parent_category column.
So you specify the parent_category in that column for each product and the name of the category in the "categories" column.
That way, the system will know which category you're talking about if several of them have the same name by checking on their parent category.