Perch 2.4 to Runway 3.1 Upgrade Process

I have an old site that I intend to upgrade from Perch 2.4 to Runway 3.1 and I am looking for any advice. The upgrade is part of a complete site redesign as it is currently not responsive, and needs many new features and content areas adding. I will be developing the new site alongside the old site on a test domain so there is no need for a conversion process on the old site if it would be easier to start from scratch. I do need to bring across 800+ blog posts, the other content can be manually added again as much of it will be changing to new templates with additional fields or features, as things like blocks were not available when this site was developed in Perch Ver 1.

Thanks for any suggestions.