Manual Backup: package all assets each of maximum 2GB size.
When creating package please make sure you don't include renditions of each image. Use package manager excludes rule to exclude rendition.
sample: I have added regex for img assets. similar you have to add different regex for other assets.
when install this package back. please make sure default asset workflow is on. so that renditions will be back when image package is installed.
There may be different approaches too.