Am I in big trouble?

Hi, new member here!

I'll take a very long story and made it short: I'm reviving a website a website we haven't done anything with in two years. We had over 1,000 blog posts that were mostly outdated (we started the blog in 2006), of low quality (selling a class, very short, etc.), or no longer relevant for our new direction.

My idea was to revise, update, and optimize the best of these posts and have the others redirect to another page...but something went wrong with the redirect plugin and the posts's URLs have changed. (Don't ask...like I said, long story.)

Right now I've bulk-edited these posts to put them into draft mode, but whether I leave them up or not, because of the URL change what it effectively means is that we have 1,000 posts that are now 404. We have like 18,000 backlinks to these posts, all now dead.

I'm not super upset about this because I'm the kind of person who likes to say "Screw it all" and start over from scratch. Out of those 1,000 posts I'd be surprised if we have 100-200 that are worth updating, and I've already started updating and republishing the best posts.

But...how much of a hit will the site take on Google thanks to my snafu, and how long might the effect last? Right now we get only 2-5 visitors from organic traffic per day anyway, but my idea was to build that back up.

Any ideas/suggestions?

Thanks so much!