What transpositions/variations are there? Looking at the position, I think d4 transposes into the open Sicilian, where the idea for white is to concede a center pawn for rapid development (the reason I sound unfamiliar with the open sicilian is because I AM unfamiliar with it).

In short:

1) Can the Open Sicilian be avoided? How?

2) Is it a good idea to actually play the Open Sicilian? Can I get away with not learning the theory? Or is it one of those "mega-theory" openings where it pays off to learn?

The move order shown looks like the Sicilian Defense: Kan Variation. 5. ...Qc7 is usually next for black after 4. e4 cxd4 5. Nxd4 .....

It can transpose in to a Scheveningen or Taimanov and probabbly others depending on move 5. ...

What are the differences between them, in terms of each sides' goals? Sorry if the question is vague, I'm just hoping to begin understanding the open sicilian from square 1.

As a similarly rated player as the OP, I recommend 3.c3 out of pfrens recommendations as white against the Sicilian.  

Usually have a nice space advantage.

The Kan is a slowly built defensive brick wall that waits for you to make a mistake against it.  It has it's faults though, f4 by white, kingside weaknesses, occasionally castling by hand and a Macrozy bind setup is possible for white.  

I used to play it as black, my coach told me to stop so I did, but I liked the Kan when I did play it.