Usually I don't buy 2nd core sets/same game and I hate it when a game forces you to do it if you want to play "as intended". But after paying less than 30CAD for my first core set (a FGS had a promotion: At the cashier you roll 1D20+1D12 and the result is your % off the retail price, I rolled 21!!!) and seeing I could buy one for 36CAD new at a LGS I couldn't resist. For a few bucks more than 2 expansions you get 3 ships, more templates, 1 more ruler, more tokens and 6 more invaluable die.
But like many already said, 1 core set to start with is enough to have tremendous fun. The simple mechanics and complex strategy make this game almost perfect!
Add a black sheet/fabric on your playing table and you're good to go! You don't have to double the core set and buy every expansions right away, just get 1 core set, setup your first game, start moving your ships and roll some dice and you'll see! Add some Star Wars soundtrack as a bonus for the mood and BAM! you'll wake up the next morning with a geek boner thinking about your last evening lol!