Hi,
about the second question, there is a ReDJ plugin option that allows you to redirect to a custom page (e.g. the site home) all error pages. In this way any called URL that should return an error is replaced with a redirect.
About the first question, you can try to prevent spiders indexing, but as I told you, the problem with Google soft errors is related to URLs internally linked (e.g. your sitemap) that you redirect elsewhere. So the best solution could be to remove reference from internal site. Try to remove there pages from the sitemap, as example.
Best regards,
Luigi