The number of pages of ads will vary depending on how many ads are currently running. How many pages of ads are displayed will also be affected by the number of ads displayed per page. If you set your filters to show only 20 ads per page, you will have far more pages than if you elect to show 50 per page. If you modify the distance radius, or any other filter, these too will have an affect on how many ads/pages are displayed.

The engine you have been watching may have been sold, or the ad may have expired. In either case, it would disappear from the active ad list.

As for email notifications on PM's, check your account settings. Click My Account at the top of any RCU page, then click Forum Settings. Find the section Private Message, and make sure you have email notifications selected.