Will having the new site (with new pages) affect the pageviews, and therefore my search engine ranking?
That question is the wrong way around. Your pageviews will not affect your SER, but your SER may affect your pageviews.
It will very probably affect it. The question is probably: How much?
You definitely want to check how many people visit your website through search engines.
SEO may improve or worsen, depending on how you do your relaunch. The most important things:
- Optimize your new site for SEO. (maybe speaking URLs, proper headlines and markup, keywords, etc etc)
- Try to keep your URLs to point to the updated content, and/or make them redirect to the updated content. If you had
/content/about and now want to use
/about, make that
/content/about now redirects to
/about with the proper HTML status code.