Older Posts

Let's break this down by your questions

Found here: https://codex.wordpress.org/Pagination

This is what a basic page template with a loop might look like. Notice the pagination functions after the loop. This will add the buttons that say older posts and newer posts, which that text can be changed.

<?php if ( have_posts() ) : ?>

<!-- Add the pagination functions here. -->

<!-- Start of the main loop. -->
<?php while ( have_posts() ) : the_post();  ?>

<!-- the rest of your theme's main loop -->

<?php endwhile; ?>
<!-- End of the main loop -->

<!-- Add the pagination functions here. -->

<div class="nav-previous alignleft"><?php next_posts_link( 'Older posts' ); ?></div>
<div class="nav-next alignright"><?php previous_posts_link( 'Newer posts' ); ?></div>

<?php else : ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>

This should be fine to use on a loop of posts, or on a single post. WP should be smart enough to figure it out. Lots of options on this document.

If used the last option on this page http://wp.tutsplus.com/tutorials/wordpress-pagination-a-primer/ to successfully add numbers to the pagination like you asked.

And finally, you can change how many posts per page in your settings tab in your wp admin dashboard. I think it's in settings >> reading and there is a menu item on that page that says something like "Posts per page" and it will say 10. You can change that number to whatever you want.

Thanks so much for the quick response! I did this, and it worked perfectly on my blog page. However, I assumed it would work the same on a custom post type page. Is this not the case? Do you know what I should be doing differently in a custom post type page? I googled it but a lot of people are say I need to do something with WP_posts as opposed to WP_Query. But I've gotten the impression from Zac that I should stick with the Query. So again, maybe I'm googling the wrong terms? (now I know pagination- so thanks for cluing me into that one :)

Thanks again for your help! I super appreciate it!

(sorry, meant that to be a comment, not an answer)