Question about Rep

So I made it to revered/almost exalted last phase and had to take a break so I missed out on WSG grind for exalted.

Do I have to do WSG till I get exalted there, or can I go to AB and get exalted there?

they are two different reps, they have nothing to do with each other

Do I NEED the WSG rep for anything?

for warsong pvp items… if you want than yes you need it if you dont than you dont