"best practice" is a terrible term :-) because it suggests there is always the "best" way to do something.

"best" is what works best *for you*.

For example:

My network is slow and unreliable. In that case, I might choose to do - generate MV on the DB that owns base tables - and refresh MV and populate over the DB links to other DB's

versus

The number of changes in my base tables is tiny and rare. In that case, I might choose to - Pull (delta) data from the source DB over the DB link and populate the MV from base_table@link_to_remote


Refresh groups can work over a db link - all they do is give you transactional consistency between a number of refresh objects

To my knowledge, you dont need to explicitly grant flashback style privs for refresh groups (even though it might be using that technology under the covers)