I am hoping Lucas really throws in the money and we get a Band of Brothers style of production value. BoB was 150 million for 10 episodes, so it would be costly for a season or more. He of course would have no problem getting advertisers so it shouldn't be a problem. This would be very heavy on plot, story, and characters, maybe more so than the trilogies, but special effects would be crucial as well as cast budgets to get people from the PT and OT occasionally.
My idea, as someone else mentioned before, would be to of course pick up a time after ROTS. I say have several story arcs going on. Some within the Empire, some outside, and maybe even a Jedi that sets some precedence for the OT that is to follow.
The Rebel Alliance name kind of implies that there may have been factions beforehand, all opposed to the Empire but seperate out of mistrust of informants and traitors among them. It would be interesting I think to tell the story of someone, perhaps Bail Organa (get Smits back into the television limelight), who must unite the factions into ONE combined force. There would be several characters of importance in this arc, such as Mon Mothma, Dodonna, and other prominent figures of the future Rebel Alliance.
Another story idea would be two friends who become seperated by political affiliation. One hates the idea of an Empire and joins one of the rebellion factions while the other joins the Empire. They both become pilots and eventually have to dogfight each other. The one who joins the Empire would be particularly interesting because we would see the inner workings of the Empire and maybe a few scenes of Darth Vader. We could also see the advancement of the TIE Fighter. It could maybe even tie in or borrow from the TIE Fighter games which were very well written.
There would be another arc much deeper in the Empire and in this we would see characers such as Piett, Jerjerod, and maybe even Tarkin. This arc would be parallel to the inner political struggles that occured within the Nazi regime and would feature alot of backstabbing and other typical political machinations. In this, we would witness the Empire as it rises completely to power.
For a final story, maybe get a lone Jedi that has been isolated for a great period of time. He returns when he feels a tremor in the Force and his story revolves around trying to discover what has happened to the Jedi and how he can restore their order. He would have to die at the end of the series, or return to isolation.
We could see Vader, the Emperor, Bail Organa and maybe even Yoda occasionally. Perhaps even a young Luke Skywalker and Leia Organa in the background. Maybe show Luke and his early interest in flying and fixing things. We could see Leia watching with keen interest as her father conducts politics.