Best way to start is get into an Open class, or similar, that doesn't have any equipment restrictions. Sounds backwards, but it's the best way to start - no limits on gear or gun.
Rear bag is very necessary, and the best one out there is the Armageddon Gear Schmedium bag, with the Heavy fill. You'll use it for more than a rear bag - most of the time, it's the only thing supporting your rifle off some of these props and barricades.
Bipod. You'll want one that cants and swivels. Alot of the things you support the bipod from are uneven. The MagPul bipod is the easiest, cheapest way to get both those features, and it doesn't need to be a QD bipod that you take on and off.
Something to keep track of your holds for different distances. I userd a wrist coach for a little while, then switched to the Cole-Tac cheat sheets that I mount to my scope tube. You're going to encounter multiple targets (8~12 per stage) sometimes at 5 different distance, shooting from multiple barriers and props. There's alot of movement, so it helps to have your distance holds right there on the gun.