Merging 5 different sites and brands into one

Hi!I am working on a new website build that will be merging 5 different sites and brands into one. There is a lot that is going into this, but I will be collaborating a bit on the sitemaps. We will have one global sitemap, and then allow the ability for uses to select topics, and see a unique sitemap. What is the best way to use analytics to help inform decisions on how to organize this and what to display or group together? Or other SEO tools, like looking at search visibility and what drives traffic, etc. I`ve been spending time in behavior flow reports and whatnot, but was just curious what ya`lls preference was when collaborting with designers on sitemaps for new sites (especially when there is consolidation involved).