Going to transition to Lightning and have a lot of Notes & Attachments? Well in Lightning, it's more about "Notes & FILES". 

Make sure to expand this post for suggestions and resources. 

So what do you do? 

1. Take the Trailhead Trail https://trailhead.salesforce.com/en/content/learn/modules/lightning-experience-productivity/work-with-notes-and-files

2. Check out the considerations for usage of note-taking tool 'Notes' and 'Files' functionality. https://help.salesforce.com/articleView?id=000337292&language=en_US&type=1&mode=1

3. Instead of using Magic Mover...Make Notes & Attachments read only and leave as a Related List. Then, gradually move the items over to Notes and Files related list. Once everything is moved over, remove the Notes & Attachments Related List and fully transition to Notes & Files. 

Be sure to check out your compliance and other regulatory rules first!