I have around 30 old posts that I want to delete on my blog. Can I just delete them permanently or should I worry about the "errors" I will get on my google webmasters tools and redirect them somehow?
You should submit a request for Google to stop indexing them as soon as possible (accessible through the Google Webmaster Tools interface). I'm sure you know the purpose of posts, but is is that important to delete them? You could just leave them as an archive as posts were originally meant for. If you don't link to them, you don't have to worry about most viewers ever seeing them, just tell Google not to index the specific ones. There's no guarantee they won't continue to be crawled, but you can keep an eye on it and if they are still getting indexed you could delete them at that time.