As far as I can tell it only really needs the fuel to maintain an L2 orbit, which is important because if it's too far away we can't really communicate with it effectively (i.e. actually download much of the data it's generating). For orientation it uses reaction wheels as you mention, and then there's a general plan to desaturate these momentum wheels by managing the average orientation of the telescope (it's effectively like an inverted pendulum: the solar wind will push it further away from having its back to the sun), but this might intefere with some observations so they may burn some fuel to maintain orientation in certain circumstances.

https://space.stackexchange.com/questions/35399/how-will-jws...

Kepler used a similar strategy (though I don't know what its desaturation strategy was): it only ran out of fuel very quickly after its reaction wheels failed.