I am currently in a project for one of my biggest clients. We have built a website that will -replace- the old website.

When it comes to actual content its is largely the same. However, the presentation of the content has changed drastically. From our point of view much more user-friendly (main reason to update the site).

Now, since the sites presentation has changed we have some major changes in:

1. HTML & CSS: To change the presentation of the content
2. URL's: To make them better understandable (301 redirects have been taken care of and are in place)
3. Breadcrumbs: To enhance the navigation (we have made the breadcrumbs match exactly with the url's)
4. Pagination: This was added to enable content browsing
5. Title tags: Added descriptive title tags to the major links and buttons.

Basically all user content including meta tags have remained the same.

Now since this company is rather successful and 90% of its clients come from Google's organic results I am obliged to take all necessary precautions. People tell me I need a migration plan to prevent the site being hurt in Google, but I have never worked using such a plan...

...So, based on the above. Would you consider a migration plan necessary and what precautions/actions would you recommend to prevent us being put down in our SERP positions?

Many thanks in advance for your answers.