When generating the template for a Document—whether it's a Quote, Order, Customer Document, and/or Business Document—you can enable the "Required Field" functionality for fields related to the Product.
To do this, access the document template you want to modify, then go to:
Fields
Quote's Product
Search for the field you want to edit
Click the pencil icon to edit
A "Edit Field" modal will open. Within Field Settings, under Basic Settings, enable the "Required field" option. Then, simply click the blue Save button.
You can repeat this same process for any other fields that you want to make mandatory.