Is this Hierarchy correct?

Why are you looking for a hierarchy and why do you first want to identify a feature, theme, or epic?

What are your thoughts about how to best approach requirements emergence and collaborative refinement with a team?

for me, anything which cant be achieved within 3-4 days, it is big (call it epic). Tasks is something which is applicable to work item (user story). In order to achieve a story, you need to work on technical work which is defined as tasks.

You might want to tag few stories which are related (feature or theme).

@Ian is right.  Why add layers on top of layers?  I coach my teams to have Stories. Yes, just stories. An Epic is any story that can't be completed in a single sprint. Break those down further.  You might find that you have Epics within Epics but the goal is to break things into units of work that can be completed in a single sprint and provide incremental value. 

I live by the 10th principle listed on the Agile Manifest for Software Development. 

Simplicity--the art of maximizing the amount of work not done--is essential.

VBMVVN TRIVARGA DHATHRI PALLA,

Scrum has no propositions on how to organize your hierarchy neither does it advocate it as a best practice. Therefore I don't think any Scrum Master would entertain spending time on this effort unless it adds value to the process. As others have already mentioned. Identify your MVP as User Stories, Requirements or any other form of a Product Backlog Item (PBI) and add details (Tasks, etc) to the most immediate work following the regular scrum ceremonies and sessions like  Backlog refinement, Sprint Planning etc. 

Make sure to constantly prioritize the backlog so the PBIs with best value are always at the top of the list.

As other have mentioned, none of that taxonomy is part of Scrum.  The Scaled Agile (SAFe) taxonomy is Theme, Epic, Capability/Feature, Story.  But that's for another forum.