The swarms of letters are Particles. AE ships with a couple of different particle systems, CC Particle World being quite powerful.
A third party plug-in like the excellent Trapcode Particular may have been used.
Other effects in this video are just Text on 3d Motion Paths; I see some Displacement effects and a lot of simple 3d transforms.
I don't think it's hard, but "hard" is a relative term ... it's not hard to me as someone who has been doing this kind of stuff for about 20 years, but it may be hard if a person doesn't yet have a firm grasp on video editing and motion graphics.