Does the number of keyword combinations used for SEO of a given website matter? Is it better to have five or thirty five?
Search engines rank pages, not websites. (But do keep in mind that since your pages will be interlinked how the other pages rank for the any given search term will indirectly affect a page's rank for those terms as well. This means you should interlink related page liberally (without forcing the issue)).
A page can rank for an unlimited number of search queries. Naturally it will rank better for some then for others.
A page generally should be geared towards one topic. If you have more then one topic then it probably should be broken up into multiple pages so each page can be optimized to rank well for keywords related to that topic.