The outer senshi don't start to appear until the last episode in Sailor Moon R, when two of the senshi have dreams in which Uranus and Neptune are in a tree. You can't see their faces, however, until they join in the next series, Sailor Moon S. Of course, they haven't joined in the NA version yet, since it only goes through Sailor Moon R.
The outer senshi are stronger than the inner senshi. During Sailor Moon S, they did not want the inners to interfere with their work of finding the talismens and protecting the planet. Of course, Sailor Moon ended up being the one that made the right decision and saved the Earth (like usual). The funny thing was that Haruka and Michiru were good friends with Usagi before they even found out she was the mendling Sailor Moon. ^_^
Of course, they eventually become friends. Especially in Sailor Moon Stars when they are constantly keeping an eye on Usagi. The outers are basically her body guards. They think they have a crybaby for a princess, but they don't really care. They protect her anyway, especially from the Starlights since they are from outside of the solar system. They also protect her from the Three Lights because they are idols. The irony, of course, is that they are the same people, which makes it even worse.
Chibi Moon is not one of the outer senshi. She shows up as a senshi around the same time period, but since she is from the moon she is not from an outer planet. ^_- No one has asked yet, but I thought I would clear that up for anyone that might be wondering.