I throw sidearm, Have since I was a kid. I have had no arm trouble, and am actually sore far less than other pitchers on my team.
As for pitches, I throw a two-seam sinking fastball, a four-seamer, a circl-change, and a sluvish type pitch. By throwing sidearm, you prevent yourself from getting a lot of 12-6 breaking pitches. My advice is this, don't get too carried away with extra breaking pitches. As a sidearmer, pitches tend to have more movement on them when throw naturally from that armslot anyway