Best practice for customizations? (Scopes, Cloning and Update Sets).

[Community Alums]

I am about to Implement the HRSD Integration with SuccessFactors.

It will require a significant amount of customization to add new Fields, new services for importing additional tables, new flows for Full and delta loads and new flow actions which can use a different alias for different environments (dev, test etc). .  I expect I will be making modifications in maybe 5 or 6 different Applications scopes.  I have three interrelated questions about best practice.  What is your experience with the following?

A.  What option do I use for managing scopes:

1. Do I create a new custom Scope and put all my customization is the new scope?   What about RCAs?
2. Do I use the global Scope only?
3. Do I put my customizations in the appropriate 5-6 scopes?  (harder to manage update sets)

B.  To clone or not to clone?

1. Do I clone items (such as flows)?
2. Or edit existing items?

C. Managing Update Sets

1. Do I use Merge update Sets?
2. Create use Batch Update Sets?
3. Do I created Update Set versions and then use the "Copy Update Set Utility" when creating a new version.

Possible Solution

I did find this post.
https://www.servicenow.com/community/now-platform-blog/best-practices-for-using-the-flow-designer/ba...
Which suggest a Best practice is:  A.1 (custom Scope);   B.1 (clone so you get updates); and C.3.

Copy Update Set Utility:  see:  https://developer.servicenow.com/connect.do#!/share/contents/3673648_copy_update_set?v=1.5&t=PRODUCT...

[Community Alums]

Thanks for your reply.  I know there is no "right" answer here.  Please see my response to Julians's post below.