The number of the items imported every time that the campaign runs is limited by the items in the source feed URL. Normally, they have no more than 10.
In any case, we do not recommend more than 3 or 5 items at a time.
Take a look at the examples in this page.
You can view the content of a feed by opening its URL in a feed reader. There are also some add-ons or complements for browsers to read the elements of the feeds.
Some WordPress feeds and other standards are paginated.
Professional Addon has advanced options for each feed, where (if compatible) you can indicate that the campaign reads all the pages of the feed by selecting the corresponding option: Check to use as multipage feed.