Multi-DB plugin & WP-Engine hosting


I just moved my wordpress multisite network to WP-Engine hosting, and I had some questions about the Multi-DB plugin.

1) Do I really need Multi-DB if i’m using WPengine?

2) Is there a way to backup all the Multi-Databases?

3) How big should the database file size be to consider installing the multi-db plugin?

4) If I wanted to undo the multi-db plugin install, can I do that?