With the scrutiny on head injuries and concussions in the professional and college hockey leagues, the helmet might well be your most important investment. This is probably the one piece of equipment you should get "new", so that you know it properly fits you. (Plus the hygiene factor; though the padding that is in direct contact with a player's head can be replaced.) As an adult player, you should get a cage. Though some of my former teammates employed all-glass shields with effectiveness, they had to bring a towel to the bench to wipe the shield down from the fog of sweat that develops. You might think that a cage would diminish the view, but it didn't when I played.
Your helmet will have straps with push-button fasteners to latch the cage to the helmet. There will also be a chin strap. Be aware that you can get replacements for these! Finally, I owned two helmets, one that was red, and another that was white. When I joined a league, our uniforms were red, so I wanted to match.
Finally, since you'll want the helmet to fit well, try these out in a store (at least to get the size)!