Hamping, no, I am not saying to enter 2800 lines in your .htaccess 
I was suggesting that you should create one general redirect rule. If only the permalink structure changed, it is possible. Could you give me an example of a URL that now returns 404, and it's new permalink?
As for the 500 errors: sometimes, when configured improperly, some .htaccess rules may cause conflicts, redirect loops and more.
You need to analyze the redirect rules you have in .htaccess.
Another approach (but it will not be a great user experience and many don't recommend it) is to 301 redirect all your 404's to your homepage. It is just an option I am not recommend it either.