Breadcrumbs are good for SEO because they give navigation structure to your website. They are also good for shoppers because they provide an easy way to go back a category to find related products.
Microdata rich-snippets are HTML tags that tell search engines details about your products. Using these rich-snippets will enhance the look of your page links in search results.
.htaccess File Redirects
You can use your .htaccess file to create redirects for old pages. This helps search engines find newer and more important pages, as well as helps your customers in case they find an old link to an old product.