When I bought into the game, I only purchased one of the Core Set (and the first Force Pack The Desolation of Hoth, but that is an aside...). I just wanted to try a new game. A few of the guys behind the counter at the hobby store mentioned more than one Core Set, but I just wanted a new game. I wasn't going to enter any major tournaments to start with.
The great thing about the Core Set is you get a lot of cards right away, and you get playable decks. Four of them to be exact (Rebel, Jedi, Sith, and Imperial). You get a taste of the other two factions (Smugglers and Spies, and Scum and Villainy), but those are really fleshed out with decks in the Edge of Darkness set (and yes, I eventually bought that too).
I generally have recommended to anyone getting into the game to start with those. Try it. See how you like it. Learn how it plays and how to build decks.
I have also bought the Force Packs as they have come out. Unlike the Core Set and the Deluxe Expansions, the Force Packs come with two of every objective set (except for the ones labeled "only one in a deck"). I have thought about purchasing an additional Core Set and an additional Edge of Darkness set to have doubles of certain cards. But I still haven't yet. Part of it is my budget. The other part is I purely play for fun with my wife and with my friends. I dont' play in cut throat tournaments. Now in my personal opinion, I think as more cards are released, the less likely it is that you have to have two of every big set. More releases, means more cards to choose from, which means more variation in player deck constructions. So though it may once have been more important to have two of sets (especially when that was all there was), I think that is now lessened.
Again, a lot of that is my opinion and personal experience, but that is what I would pitch to any new player.