[DELETED]

Well the total number of pages you only need to take into account should not exceed to 50,000 thousand pages for per sitemap.
If the number of pages in your website is increasing then you must divide your sitemap as per type of pages. You can divide the page by:-
Category Wise
Product Wise
And you can also divide your sitemap by page type or content type, by this you can increase the number of pages in the sitemap & also increase its visibility on search engine.

[DELETED]

You can add many pages in your single sitemap but for the best Result if you have largest site Like Ecommerce you need to Design Sitemap Category Wise and Link your All site map with your Main Site Map.
This will help Search Engine to Easily Accesses Your Website and index your Web page Category Wise.

By far the best method would be use WordPress to implement your website, and to use a free Google XML Sitemap Plugin to automatically create the very best type of sitemap, that Google loves, in the format they love most, every time you make any changes.

That's what I'd recommend!

Chris

The optimal number would be zero. You don't need a sitemap.

Google does not love sitemaps.

Paul

You can add many pages but the end result will be confusion for its user. Although the site must be user friendly. Try to categorize the site map.
Make it as simple you can and place a link in every page to return back to home page or from where it has started.
Good Luck..!!!