Big image tables maintenance

I have a 10 TB size table with multiple bytea columns (image & doc)and makes 20TB of DB size. I have a couple of issues to maintain the DB.

1. I Would like to separate the image column from the 10TB size table, place it in a separate schema. The change should not result in any query change in the application.  Is it possible? Doing this it should not affect the performance. 

2. I can't maintain files on File system as the count is huge, so thinking of using any no-sql mostly mongo-DB, is it recommended? Or PostgreSQL itself can handle? 

3. Taking the backup of 20TB data, is big task. Any more feasible solution other than online backup/pg_dump?

Each image retrieval is 

Currently, we are on pg 9.4 and moving to 10.5 soon.