Transferring a site from Instantcms to WordPress, how to avoid SEO problems?

Question

Search Engine Optimization

There is an old site (almost 5 years old), with good performance in the PS:
Pages indexed: more than 20 thousand
TIC: 600, PR: 4 in Yandex at least. Tell me, is it desirable to save all the URL paths on the site? Those. URLs for sections, subsections, and of course articles?

Answer 1

htaccess + plugin Redirection

Answer 2

This is important, positions can completely disappear when changing urls