I agree about μετά αυτόν; right away it seemed foreign somehow (but my experience is pretty limited so take it with a grain of salt
). I would have tended towards using an adverb, perhaps ταχέως.
However, for the verbs the aorists ανέβησαν and (κατ)έπεσαν would seem to be called for, since the actions of going up the hill and coming back down are seen as completed actions, not going on while other things are happening.
One other thing: Ιυλιάνης is a masculine ending (or else a genitive singular, which doesn't fit the context here). I'm the last person on Earth who'd take issue with that
, but if you're going for an exact translation then perhaps Ιουλιάνη would be better. (I don't know how to pronounce the ιυ sequence so I changed the beginning a little.)