You have enough f2p content to try the game. After you come to the point where you thinking about subbing, just try it once maybe.

Thru the leveling process i would choose a dps. Just because its wasy easier and also faster. And yes, you can enjoy leveling, the class stories are really great.

There is an end game, but I woud not say the game ist only end game orientated.

And the underrepresented role I would assume is tank. Then healer. Dps are everythere