@WeezyYe
If you become a subscriber you will get access to level to 65 and all DLC's that include Rise of the Hutt Cartel, Shadow of Revan plus the current 13 chapters of Knights of the Fallen Empire. If you buy just shadow of revan DLC, you will only get access to level to 60, and only have Rise of the Hutt Cartel and Shadow of Revan DLCs only and you also won't be a sub or have access to Knights of the Fallen Empire.
Personally I'd recommend to become a sub, even if it's just for a month and get full access to max level and the currently released chapters. Another option is to purchase a bundle such as:
http://www.amazon.com/Star-Wars-Republic-Knights-Starter/dp/B00T8NURF8
This gives
All DLC's include Knights of the Fallen Empire
90 Days subscription
2400 Cartel Coins for the Cartel Market
In-game Pet: Juvenile War Rancor