My organization uses JIRA and I feel its one of the best tools I've ever used.

1. Do you use a tool to capture and management? what tool? what tools are available for such?

JIRA (other tools - IBM RTC, Mingle, Trello)

2. Do you capture and manage manually i.e. word documents, spread sheets etc? do you have templates to share?

If using tool like mentioned above, would not manage in Word document or Spreadsheet. If I've to (given no tool is available), then in word or spreadsheet - but these ideally should be in sharepoint. 

Templates vary per project. Ideally table with columns: UseCase#, AS A, I WANT, SO THAT 

3. in the management of US do you assign unique numbers to each US? 

Tools would assign unique numbers. Otherwise, US1 for main components. US1.1 for sub components.

4. Do you versions them?

Of course!

5. How do you align Acceptance Criteria, Test Cases to your US? 

Acceptance criteria should signify what is the acceptable quality of the US output.

6. How do you know when you have an epic and not a US?

Thumb rule: If the US cannot be completed in a sprint (or 2), its too big (epic).

7. How do you decompose the user stories into smaller sets of US?

Read: Mountain Goat SPIDR user story splitting techniques

8. How do you generate and document technical stories from existing US?

What kind of technical stories? My frontend stories have backend API to be implemented. I write acceptance criteria for API functionality.