Another option is to look at Atom, which is another format read by all modern readers transparently (no one will notice this is Atom or RSS). Atom has pagination as per this RFC. Generally, though, pagination is not widely used to say the least... so you probably don't need to bother too much!
Whether you pick RSS or Atom, it's useless to make your feeds "too large". Stick to a small-ish number of items, between 10 and 20, depending on how often you publish items.
Also think about implementing PubSubHubbub which is a fairly simple publish/subscribe protocol which will let anyone interested in your content know that a given feed has updated.
