Archiving blog into static read-only site

Hello,

One of the blogs that I manage has become severely bloated given that it has 1000+ posts and several thousand comments.

What I am looking to do is, replace it with a fresh installation of WordPress for my readers. However, I would like to have the current version of the site still accessible.

Hence I would like to:
Convert the existing site into a read-only site where readers can go back and view the old archives
Convert the entire site if possible into a static website where very little work is actually done by the server in terms of running queries and generating content on the fly

Caveats:
The theme I am using uses tim thumb so it dynamically generates thumbnails for the posts. How can I ensure that images are visible on the site and yet at the same time tim thumb no longer generates image thumbnails on the fly?

Would greatly appreciate any help to achieve the result I’m looking for. Any leads would be helpful