Retire/archive old posts before theme redesign

Do you have any recommendations for a clean way on how this could ideally be done?

We are embarking on a news website redesign…

1.) For the redesign, we don’t want to carry over all the old content/posts for simplicity. Only select posts (maybe 4-5) should appear on the new site homepage that will have a brand new theme.
BUT
2.) We still need to archive the 1,000 or so old posts because those URLs are still used by the authors in their portfolios. The added caveat would be if these old URLs will show the stories in the old theme format, rather than what we’d predict would be a poor adaptation of old content appearing on the new theme story format.

Thanks for your help.