404 redirects

Hi everyone, I’m looking for some advice on addressing 404 errors. I currently have 854 of them... yes, I know that’s a lot! The reason is that we switched our site and didn’t set up redirects (rookie mistake, I know). To be fair, I’m the only one in charge of SEO. I have access to all the links, but I need to either set up redirects or remove them. From what I’ve researched, it’s important to have a 404 page (which I already have), but I’m wondering what to do next. I’ve read that it’s best to keep redirects minimal, which is my plan, but I also know that 404 errors can hurt SEO. Should I put them in a robots.txt file, or is there another best approach for this situation? What are the best next steps?