With proper redirects and technical execution, most sites maintain or recover rankings within four to eight weeks.

 Where possible, yes. If you must change URLs, 301 redirects are mandatory for preserving ranking signals.

Sending all old URLs to the homepage via a redirect rather than mapping each to its specific equivalent new page.

Only if absolutely necessary. Domain changes add a significant layer of SEO risk on top of the redesign itself.

Use a dedicated redirect checking tool to verify every old URL resolves to the correct new URL with a 301 status code.