In sandboxes with Summer '20, they've made using the Salesforce Optimizer easier. It's now an app and the information is viewable in your org (versus PDF output).
I bring this up because this can be useful to point out what objects you're pushing limits on and whether best practice is a lower number.
To directly answer your questions, there's the process ...
Email Alerts and Tasks can be created as many as you can on an Object. I am also providing a few links below as they can be useful for you:
In our case I checked Setup > Background Jobs
There was a Job Type there called "Cleanup of custom field data when a custom field definition is hard deleted"
The Status showed "Completed" so I retried my deployment validation and this time it completed successfully.