MTG Salvation

This has probably already been asked a bunch of times, so sorry if the question is annoying. I just recently started playing Magic with some friends and I was wondering what would be the best way to expand my card collection. I don't think I'm quite at the point where I should be buying singles, even though I've been told it's generally the optimal thing to do. I already own a Shadows Over Innistrad Deckbuilder's Toolkit and I went to my local game store and bought a $5 randomized card pack with 200 cards from recent sets (no lands, all black cause that's my fav of the 5 colors, and only commons/uncommons). I was thinking maybe a fat pack would be a good choice? I could use some extra lands and boosters are always nice cause I want some more rares xD. But even then, I'm not sure which Fat Pack I'd buy. Journey into Nyx seems sooooo cool and I love the constellation mechanic so maybe that one. Or maybe I'll go back to my game store and buy a green or white 200 card pack--both of which are tied for my 2nd fav color--despite the fact that I won't get any rares. What do you guys think???