Disavow spam domains

One of my domains got a negative seo attack.
Some college had the same attack with backlinks from different domains.

Is it a problem If we merge the disavows, and upload for the sites?
I mean, Is that a problem that I have a bunch of domains (approx. 1000 domain) in my disavow, where my site may havent appeared in the first place?

Including domains in your disavow list that may not have links to your website should be fine. If you know that spam links might come from some domain in the future, preemptively disavowing is fine.

You might read this thread too:
https://www.blackhatworld.com/seo/is-this-a-negative-seo.960888/