For season 3 (or just patch 2.2) i will be using 4x WW barbs, ive seen gameplay videos and it looks amazing

For barbs if you plan to do infinite wrath, i believe its completely immune to all CC so...couple that with whirlwind which moves through mobs unhindered, you should be completely fine.

I leveled up a few barbs just recently, i dont plan to play season 3 since im not interested in any of the s3 items yet

Leveling speed is completely determined on your skill to keep characters sync'd, after that its just playing 1 character (sorta)
i found WW barb to be the easiest to keep sync of, other than that a leap style barb, hold shift and leap, ground stomp with pull effects, cleave, rend...being a melee character and having to "chase" mobs ends badly for me

With only 2 characters though you should have a much easier time keeping characters sync'd, after that it really is just standard diablo, gearing and progression