Is it possible to create a single global custom module, create several fields (such as rich text) and call on those fields instead of the whole custom module? I gave the developer documentation a go but couldn't seem to find a straight answer.
Are you trying to access only the field value, and then insert that into the HTML? That's possible if you copy the value only for that field. So if for example you have a rich text field labeled "My rich text" and internally named "my_rich_text", you can access the value from within the custom module with {{ module.my_rich_text }}. So in the HTML + HubL field, that might look something like: