sitemap for users not search engines
There is a module that does what you want, and it isn't XML Sitemap but just Sitemap:

https://www.drupal.org/project/sitemap


  This module provides a site map that gives visitors an overview of
  your site. It can also display the RSS feeds for all blogs and
  categories.
  
  Drupal generates the RSS feeds automatically but few seems to be aware
  that they exist.
  
  The site map can display the following items:
  
  
  A message to be displayed above the site map.
  Any books.
  Any menus that will be displayed fully expanded.
  Any vocabularies, with all the terms expanded. Optionally with term depth, node counts, and RSS feeds.
  A syndication block, the "more" link goes to the site map.
  


Then:


  because the site already has too many modules?


There is really no way to quantify this for you. There isn't necessarily a module limit, your limit is defined by the limits of your hosting space. The performance impact of adding the Sitemap module, vs spending hours doing it yourself (to reach the same point but with 10x the maintenance) is negligible, especially since you can cache it in Drupal and use things like Varnish or Memcache if your host supports it (if not, find an updated host!). You will be fine.