The original version covers up to level 50, while the expansion raises the level cap to 60 and adds 3 new jobs only available by having at least one level 50 of the prior jobs/classes.
Not being able to chat in global channels is an RMT (real money trading) countermeasure, I am unsure atm when or how this restriction lifts, probably by completing the trial and suscribing to the game. You may want to look out for shouts in your area for FC (free company aka guild) recruitments, to meet more players and make friends.
About the armoury system: you start the game with one class and once you reach level 10 (and always completing your class quests which are every 5 levels), you have the option to visit other guilds in the city and unlock more classes. At level 30 your class will turn into a job with extra skills and attributes, you will see the requirement to unlock that job by talking to the corresponding class NPC.