RSS 2.0 Specification:
In RSS 0.91, various elements are restricted to 500 or 100 characters. There can be no more than 15 s in a 0.91 . There are no string-length or XML-level limits in RSS 0.92 and greater. Processors may impose their own limits, and generators may have preferences that say no more than a certain number of s can appear in a channel, or that strings are limited in length.
In RSS 2.0, a provision is made for linking a channel to its identifier in a cataloging system, using the channel-level category feature, described above. For example, to link a channel to its Syndic8 identifier, include a category element as a sub-element of , with domain "Syndic8", and value the identifier for your channel in the Syndic8 database. The appropriate category element for Scripting News would be 1765.
An RSS file is primarily used to tell subscribers when there's is new content on your site. You would generally set the number of s in your feed to reasonably accommodate the number of pages that change on a regular basis over a certain period.
If you want the SEs to know about your pages then another type of XML file would be suggested; site maps.