I am transferring a website over from static to CMS and the new CMS will have the same URL structure. Do I need to do any 301 redirects or anything else so I don't impact current ranking. Also if I do find url differences how long should the 301 redirects be kept for.
This applies to your situation:
- If the domain is the same go to 2.
- If the url's are the same, go to 3.
- Do nothing and enjoy.
You only ever need to use a 301 redirect when changing domain or a url. In the event that you do need to use a 301 redirect then you need to have that as long as the URL exists, its not a tell Google once then remove it... keep it forever.