How to show a post single post in page template

Currently I’ve divided posts into 5 different categories, based on the categories I’ve created 5 page templates. all of the pages are listed into the home page navigation menu. in my home page I’m showing 5 posts in five different categories. when they clicked a post that post will shown in the single page template(that’s what word press normally does) but i want to show that post into my page template. because each page template having different designs. if there is any way to set the permalink to point to the page template and show the post in to full.

posts_per_page & pagination conflict

I have a custom query to display my custom post type. posts_per_page set to ‘5’. In admin post per page set to ’10’ (settings => Reading => Blog pages show at most 10 posts)
My template lists 5 posts per page. If I have 15 posts it must be shown in 3 pages, but on third page I get 404 error. So my pagination uses the admin settings (10 posts per page). How can I fix it?