Can Webflow CMS be used as a Database?

Have you seen Web design lessons | Webflow University and ► [LIST] Feature Availability & Limits?

Short answer to all of your above questions: No.

Longer answer:

Not natively just using pure Webflow. Imagine Webflow as the creator tool for the front-end of your website. Only basic CMS is allowed - what is currently supported is explained in the Articles link above. If I require additional features, I currently export and get a web developer to integrate with Wordpress.

Can code be utilized to manipulate the CMS to interface

To a certain extent. You have to use the custom code field with the CMS, and get your web developer to write custom JavaScript code for that.