[font="Comic Sans MS"]I believe 5 cr request is not that huge. We have a setup with transactional replication that transfers millions of records for reporting purposes each day. As per your client requirement you need bidirectional flow of data so I would suggest to go with "Transactional Replication with Updates". I still don't understand the need to go for Merge Replication, you only would complicate things as it's kinda difficult to manage, and the requirement which you've provided doesn't support that either.

Check on BOL for more info.[/font]